Add some docs and return shape ref on manual add
Add some docs and return shape ref on manual add

Add documentation to many functions. Have addCircle and addRectangle
return a reference to the tracked shape to the client.

Add the following undocumented terms to the project:
* Tracked Objects
* Schema: ShapeData
* Schema: Builder JSON

TODO: Document the above undocumented terms.

iFixit/node-markup,iFixit/node-markup,iFixit/node-markup