Merges context-refactor branch.  Addresses issue #9.

This API-breaking change makes rendering contexts modular.  Updates
tests and docs and adds new docs.  Please see docs/upgrading.md.

Squashed commit of the following:

commit 7d5289341e5281971ede097c5c1c8213c85a2412
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat May 19 23:11:26 2012 -0700

    Updated the doc examples for the new API.

commit 103ec664ccdd777ff314cc5f812b2ab0c05a5086
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat May 19 22:44:35 2012 -0700

    Markdown fix attempt.

commit 488e302fcdf7bb2c61f60fe1df0d825bcb1ec17e
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat May 19 22:40:30 2012 -0700

    Added an upgrade guide.

commit 22eda0d675831f1a4aa7d4d84d4fe538e84391c8
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 18 23:38:36 2012 -0700

    Canvas renderer docs, added constructor-time context defining to Actors.

commit c77b67ef2aa31043d465e0188215a0702bf046f1
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 18 23:18:44 2012 -0700

    Doc formatting fix.

commit 132db1e83b7b9662b10f2f894e8cdce2d7a1f025
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 18 23:16:55 2012 -0700

    Updated DOM README.

commit c9224f5961328135e32fefe7fe092493d081c38a
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 18 22:56:57 2012 -0700

    Link URL fix.

commit 285fcacf79e6be790a6a6e68b0509504542c6fab
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 18 22:54:43 2012 -0700

    Markdown fix.

commit 9d903390b4024eff52cd4878e35a69c184beedb9
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 18 22:52:42 2012 -0700

    Added a note about Kapi.Actor being a base class.

commit e0817d61e385fbb88ad3b6187e53c4a85ef56c2e
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 18 22:39:12 2012 -0700

    Added documentation about contexts.

commit 25917553e1816ef0ab059db0f8823e05db2c9760
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu May 17 22:31:53 2012 -0700

    Getting start doc tweak.

commit b5e750b9edd472cc7304cf027707dbec878acaab
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu May 17 22:24:18 2012 -0700

    Changed the URL paths in docs/README.md.

commit 1e9e71779a252a0cba6712654c05233e08913b3b
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu May 17 22:20:57 2012 -0700

    Moved the controller methods to their own file.

commit 9afe34b3cf82b9e36f54f78a36aeb9dd75810436
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Thu May 17 22:03:09 2012 -0700

    Moved the getting started guide to its own file.

commit 2348875f583380696e809ccb78e0fde549b5cfed
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 22:54:25 2012 -0700

    README updates.

commit 40b00420ae95f9b3b2896cb19b1963b869463726
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 22:41:10 2012 -0700

    Made updates to the README for the new API changes.

commit 7f35c74b23d1c317f2209605d8f273fba2687bd1
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 21:47:55 2012 -0700

    Actor extension cleanup and annotations.

commit 1a6e1cbb0ad7e879c7193ffaa6a031cf9e9258b8
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 21:23:11 2012 -0700

    Minor rekapi.actor.js cleanup.

commit 95d8a9b9d5b30a7188f4f9ed4c806128575b664a
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 21:12:31 2012 -0700

    Small core cleanups.

commit db2f23183f72773108ee402b29321a7dba11696c
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 20:59:09 2012 -0700

    Updates the bubbles demo for the new API.

commit 856d07f121831e241535b8a7159ff69821ec27b4
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 20:45:53 2012 -0700

    Rebuilds 0.8.0.

commit e6bb428a50238c2ff17e9546b5bd0b8a1d536380
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 20:45:06 2012 -0700

    Updates the Pie demo, minor library cleanup.

commit 64c1a9e5a4d00fd9dc5bef0a2b18877cf6c16e70
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Wed May 16 20:02:07 2012 -0700

    Removes cnavas elements from unit tests, fixes the AMD test.

commit 5c4ee1f9404057699919108ce677d168c63d373f
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Tue May 15 22:26:07 2012 -0700

    Fixed some clearing-related bugs.  Fixed the bargrapgh demo.

commit 492698e4e35684e9cb31db9bfc5bddac08e847bc
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Tue May 15 22:20:52 2012 -0700

    Partial update of bargraph demo; build script fix.

commit 52af39b455c376f6cc87f9ed7795011306305fb2
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Tue May 15 22:01:29 2012 -0700

    Updates the build script and catimate demo.

commit c1ba620418831f04ba0af77e6891cedca9295deb
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Tue May 15 21:44:55 2012 -0700

    Moved the canvas context docs to their own README.

commit 6daf7b3e6139430b3107fc1df079ada79cfc5ed5
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Tue May 15 21:31:19 2012 -0700

    Updated all tests to pass again.

commit bfe156815530c4ea2fcb6d1d134c4f7e7fb77703
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Mon May 14 20:29:25 2012 -0700

    Fixed tests in test.color.html.

commit dcd151d609b263def8f3e8fbdc02aeb95b1a7591
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Mon May 14 20:22:26 2012 -0700

    Fixed tests in test.state.html.

commit c9f83424283619f9556304246d62feb22e1c334f
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Mon May 14 20:01:50 2012 -0700

    rekapi.dom.js -> rekapi.dom.actor.js

commit 3e71337bb348c5f47afb134c4046b96921e793be
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Mon May 14 19:56:08 2012 -0700

    rekapi.dom.js cleanup.

commit 865a2dc634a9cc5042b4da3b371fef90dadbeba0
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 23:02:55 2012 -0700

    Refactored DOMActor to use proper Actor inheritance.

commit 757f8c13cb306dafd506fe7a35f2a3969905c0a6
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 22:35:29 2012 -0700

    Removes parent styling from rekapi.dom.js.

commit d0335a60441d187c4212fd8af8bd2ac6d2b02d28
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 20:28:04 2012 -0700

    Fixed parameters on test.dom_doesitlookright.html.

commit e355c6ab8bb89a7ae25f4f93b685838798160c1a
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 16:55:43 2012 -0700

    Minor cleanup.

commit 8d155f616f0ab50144478f18173a41305987f059
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 16:52:35 2012 -0700

    Removed rekapi.canvas.js.

commit 8e362979c44dfef18fde071b57f8a2a629b6f0d4
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 16:45:29 2012 -0700

    Created the CanvasActor subclass.

commit fc84b08e7fc5bf270f866dedb9dae0bd0661264a
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 16:31:56 2012 -0700

    Got frame cleaning to work again.

commit 88744ed034a080676ba260f2714757c9e055898f
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun May 13 16:21:50 2012 -0700

    Got some semblance of an animation working again.

commit 7a8727a2f74ec348590f96295c121b4f6b1f89ba
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat May 12 16:06:34 2012 -0700

    Changed and fixed some things to make them less broken, although they are still broken.

commit e583b7f86b4279129bf8d28842fdfe103a1a1d0b
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat May 12 15:51:43 2012 -0700

    Added files that I forgot to in the previous commit.

commit ee26e5062c3026e4e1ecf0bcb8c783f2e89cd3c0
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sat May 12 15:51:08 2012 -0700

    Adding lots of unfinished code that breaks everything.

commit a36dca41433c2103801cb8813e61b78eec167a6e
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Fri May 11 20:34:09 2012 -0700

    Started on an incomplete refactor, things don't work.