Documentation generation prototype

[jonathanolson]

Checked into existing JSDoc parsers, and it seems like all miss some aspects of how we structure code (for example, public tags won't catch 'scenery-internal' and so would be displayed, how we use inherit to set instance and static members, how we use ES5 setters/getters, etc.)

I'm adding some code to generate documentation as a solution for now (at least useful for dot/kite/scenery, as I ran into a ton of things that otherwise would need manual generation during issues like phetsims/dot#38).

It uses esprima to parse to a general AST, then extractDocumentation.js to turn this into a PhET-style-specific "AST"-like documentation object, and then documentationToHTML.js to create index/content HTML. See Dot's gruntfile for an example of how I'm currently generating Dot's documentation (which was close to barren before).

[jonathanolson]

Tagging to discuss this approach (and its constraints) vs. other approaches.

[samreid]

I had some questions about documentation.js that I asked over in this scenery issue: phetsims/scenery#499