add a package.json

so that users can

```
npm install --save github:NeilFraser/JS-Interpreter
```

closes NeilFraser#156

package.json

@@ -0,0 +1,16 @@
+{
+  "name": "js-interpreter",
+  "version": "0.0.1",
+  "description": "A sandboxed JavaScript interpreter in JavaScript.  Execute arbitrary JavaScript code line by line in isolation and safety.",
+  "main": "interpreter.js",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/NeilFraser/JS-Interpreter.git"
+  },
+  "author": "Neil Fraser",
+  "license": "Apache-2.0",
+  "bugs": {
+    "url": "https://github.com/NeilFraser/JS-Interpreter/issues"
+  },
+  "homepage": "https://github.com/NeilFraser/JS-Interpreter#readme"
+}