Initial pass at adding codemirror

Adds a fairly basic configuration suited for markdown.

We can do syntax highlighting for more languages in embedded
code blocks by including more modes, but it's already
7 separate source files -- we probably need to package it
up if we want more (or dynamically load them).

Closes #76

static/codemirror/addon/edit/continuelist.js

@@ -0,0 +1,101 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: https://codemirror.net/LICENSE
+
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") // CommonJS
+    mod(require("../../lib/codemirror"));
+  else if (typeof define == "function" && define.amd) // AMD
+    define(["../../lib/codemirror"], mod);
+  else // Plain browser env
+    mod(CodeMirror);
+})(function(CodeMirror) {
+  "use strict";
+
+  var listRE = /^(\s*)(>[> ]*|[*+-] \[[x ]\]\s|[*+-]\s|(\d+)([.)]))(\s*)/,
+      emptyListRE = /^(\s*)(>[> ]*|[*+-] \[[x ]\]|[*+-]|(\d+)[.)])(\s*)$/,
+      unorderedListRE = /[*+-]\s/;
+
+  CodeMirror.commands.newlineAndIndentContinueMarkdownList = function(cm) {
+    if (cm.getOption("disableInput")) return CodeMirror.Pass;
+    var ranges = cm.listSelections(), replacements = [];
+    for (var i = 0; i < ranges.length; i++) {
+      var pos = ranges[i].head;
+
+      // If we're not in Markdown mode, fall back to normal newlineAndIndent
+      var eolState = cm.getStateAfter(pos.line);
+      var inner = CodeMirror.innerMode(cm.getMode(), eolState);
+      if (inner.mode.name !== "markdown") {
+        cm.execCommand("newlineAndIndent");
+        return;
+      } else {
+        eolState = inner.state;
+      }
+
+      var inList = eolState.list !== false;
+      var inQuote = eolState.quote !== 0;
+
+      var line = cm.getLine(pos.line), match = listRE.exec(line);
+      var cursorBeforeBullet = /^\s*$/.test(line.slice(0, pos.ch));
+      if (!ranges[i].empty() || (!inList && !inQuote) || !match || cursorBeforeBullet) {
+        cm.execCommand("newlineAndIndent");
+        return;
+      }
+      if (emptyListRE.test(line)) {
+        var endOfQuote = inQuote && />\s*$/.test(line)
+        var endOfList = !/>\s*$/.test(line)
+        if (endOfQuote || endOfList) cm.replaceRange("", {
+          line: pos.line, ch: 0
+        }, {
+          line: pos.line, ch: pos.ch + 1
+        });
+        replacements[i] = "\n";
+      } else {
+        var indent = match[1], after = match[5];
+        var numbered = !(unorderedListRE.test(match[2]) || match[2].indexOf(">") >= 0);
+        var bullet = numbered ? (parseInt(match[3], 10) + 1) + match[4] : match[2].replace("x", " ");
+        replacements[i] = "\n" + indent + bullet + after;
+
+        if (numbered) incrementRemainingMarkdownListNumbers(cm, pos);
+      }
+    }
+
+    cm.replaceSelections(replacements);
+  };
+
+  // Auto-updating Markdown list numbers when a new item is added to the
+  // middle of a list
+  function incrementRemainingMarkdownListNumbers(cm, pos) {
+    var startLine = pos.line, lookAhead = 0, skipCount = 0;
+    var startItem = listRE.exec(cm.getLine(startLine)), startIndent = startItem[1];
+
+    do {
+      lookAhead += 1;
+      var nextLineNumber = startLine + lookAhead;
+      var nextLine = cm.getLine(nextLineNumber), nextItem = listRE.exec(nextLine);
+
+      if (nextItem) {
+        var nextIndent = nextItem[1];
+        var newNumber = (parseInt(startItem[3], 10) + lookAhead - skipCount);
+        var nextNumber = (parseInt(nextItem[3], 10)), itemNumber = nextNumber;
+
+        if (startIndent === nextIndent && !isNaN(nextNumber)) {
+          if (newNumber === nextNumber) itemNumber = nextNumber + 1;
+          if (newNumber > nextNumber) itemNumber = newNumber + 1;
+          cm.replaceRange(
+            nextLine.replace(listRE, nextIndent + itemNumber + nextItem[4] + nextItem[5]),
+          {
+            line: nextLineNumber, ch: 0
+          }, {
+            line: nextLineNumber, ch: nextLine.length
+          });
+        } else {
+          if (startIndent.length > nextIndent.length) return;
+          // This doesn't run if the next line immediately indents, as it is
+          // not clear of the users intention (new indented item or same level)
+          if ((startIndent.length < nextIndent.length) && (lookAhead === 1)) return;
+          skipCount += 1;
+        }
+      }
+    } while (nextItem);
+  }
+});

static/codemirror/addon/mode/overlay.js

@@ -0,0 +1,90 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: https://codemirror.net/LICENSE
+
+// Utility function that allows modes to be combined. The mode given
+// as the base argument takes care of most of the normal mode
+// functionality, but a second (typically simple) mode is used, which
+// can override the style of text. Both modes get to parse all of the
+// text, but when both assign a non-null style to a piece of code, the
+// overlay wins, unless the combine argument was true and not overridden,
+// or state.overlay.combineTokens was true, in which case the styles are
+// combined.
+
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") // CommonJS
+    mod(require("../../lib/codemirror"));
+  else if (typeof define == "function" && define.amd) // AMD
+    define(["../../lib/codemirror"], mod);
+  else // Plain browser env
+    mod(CodeMirror);
+})(function(CodeMirror) {
+"use strict";
+
+CodeMirror.overlayMode = function(base, overlay, combine) {
+  return {
+    startState: function() {
+      return {
+        base: CodeMirror.startState(base),
+        overlay: CodeMirror.startState(overlay),
+        basePos: 0, baseCur: null,
+        overlayPos: 0, overlayCur: null,
+        streamSeen: null
+      };
+    },
+    copyState: function(state) {
+      return {
+        base: CodeMirror.copyState(base, state.base),
+        overlay: CodeMirror.copyState(overlay, state.overlay),
+        basePos: state.basePos, baseCur: null,
+        overlayPos: state.overlayPos, overlayCur: null
+      };
+    },
+
+    token: function(stream, state) {
+      if (stream != state.streamSeen ||
+          Math.min(state.basePos, state.overlayPos) < stream.start) {
+        state.streamSeen = stream;
+        state.basePos = state.overlayPos = stream.start;
+      }
+
+      if (stream.start == state.basePos) {
+        state.baseCur = base.token(stream, state.base);
+        state.basePos = stream.pos;
+      }
+      if (stream.start == state.overlayPos) {
+        stream.pos = stream.start;
+        state.overlayCur = overlay.token(stream, state.overlay);
+        state.overlayPos = stream.pos;
+      }
+      stream.pos = Math.min(state.basePos, state.overlayPos);
+
+      // state.overlay.combineTokens always takes precedence over combine,
+      // unless set to null
+      if (state.overlayCur == null) return state.baseCur;
+      else if (state.baseCur != null &&
+               state.overlay.combineTokens ||
+               combine && state.overlay.combineTokens == null)
+        return state.baseCur + " " + state.overlayCur;
+      else return state.overlayCur;
+    },
+
+    indent: base.indent && function(state, textAfter, line) {
+      return base.indent(state.base, textAfter, line);
+    },
+    electricChars: base.electricChars,
+
+    innerMode: function(state) { return {state: state.base, mode: base}; },
+
+    blankLine: function(state) {
+      var baseToken, overlayToken;
+      if (base.blankLine) baseToken = base.blankLine(state.base);
+      if (overlay.blankLine) overlayToken = overlay.blankLine(state.overlay);
+
+      return overlayToken == null ?
+        baseToken :
+        (combine && baseToken != null ? baseToken + " " + overlayToken : overlayToken);
+    }
+  };
+};
+
+});