added new line,circle, and image objects to the API

Ignore-this: 35ed92d703772ecf9efea8dfd8deb420

These objects can be used to manipulate what is seen on a draw object.
This should make for much smoother graphics updates and no longer needing to call
draw:clear() on every update.

darcs-hash:20141210152803-c21fe-d8e9810a258d6ad59ab5c0ced9b44332ca7faa6e
updated the API reference to include the new draw primitives

Ignore-this: b2e38504dc49fb8aef51274ac66626d1

darcs-hash:20141210153015-c21fe-936c5dbc56acdc712bbe047734c5f66e2eeef627
updated the pong example to use the new draw primitives

Ignore-this: 56e17dd06c6370704711c33bf69e927e

Now pong should not flicker at all on slower machines.

darcs-hash:20141210153052-c21fe-e99680bbab0f65c9b24ce6682753c1a892677b1d