docs: improve grammar & formatting, plus add TSConfig Reference links

[agilgur5]

Summary

Improve grammar and formatting in the README, as well as add several TSConfig Reference links.

Details

• improve grammar in several places

  • mostly add "the" and commas in several places where they were missing
    • and put a period or semicolon in a few places where there was a comma splice
    • for "deep merge", parens were used, whereas a colon is a better fit
  • consistently use "(see #x)", instead of sometimes using parens and other times using commas
    • also change "only if useTsconfigDeclarationDir" to "unless useTsconfigDeclarationDir" for clarity
      • have looked at this many times and thought something was unintuitive about this: useTsconfigDeclarationDir defaults to false after all
  • "typescript" -> "TypeScript" as a proper noun
  • "js" -> "JS" similarly
  • "es6" -> "ES6"
  • "rollup" -> "Rollup"
  • "rollup watch" -> "Rollup's watch mode"
  • "work directory" -> "working directory" (that's what the "w" stands for)

• improve formatting in several places

  • split up paragraphs a bit more neatly as a single new line in Markdown is just rendered as a space
    • similar to my previous PR for emitDeclarationOnly (feat: support emitDeclarationOnly #366)
      • and apparently I missed two sentences in the "Declarations" section there too
  • for tsconfig, objectHashIgnoreUnknownHack, and typescript, actually add a double new line
    • to break up the paragraph for better rendered readability
  • don't skip heading level for "Some compiler options" -- this should be an h3, not an h4
    • remove inconsistent period in one of the headings as well (and headings aren't normally supposed to have periods)
  • consistently use backticks when referencing plugin, tsconfig options, etc
    • e.g. tsconfig, include, exclude, node_modules, etc
      • also, for allowJs, put the proper **/node_modules/**/* exclude as an example similar to the **/*.js+(|x)
        • as plain node_modules won't work as I found out in failed to transpile tslib.es6.js after update to v0.30.0 #264 (comment)
  • consistently use 1 tab indent for plugin options' descriptions, instead of a few 2 tab indents
  • for "Requirements" section, use bullets instead having everything on one line
    • the way it was written seemed like they were intended to be on different lines, but a single new line in Markdown is just rendered as a space (per above)
      • bullets are a little better than just new lines as well

• add TSConfig Reference links to several tsconfig options mentions

  • extends, declarationDir, declaration, declarationMap, and emitDeclarationOnly
    • also added the mention of extends in "chaining tsconfigs"

Misc

Been staring at the docs for a while and making edits slowly; finally wrote up a PR for it.
Also helps to look at the docs on NPM instead for a change of visuals to have less tunnel vision