Add support for multiple render targets.
Fix everything that uses a framebuffer with a color attachment.
Add Context tests.
Fix Framebuffer tests.
Add tests for multiple render targets.
Updates from review.
Make Framebuffer immutable.
Fix typo.
Update code and tests to make framebuffers immutable.
Merge branch 'master' into mrt
More updates from review.
Add test for clearing framebuffer with multiple color attachments.
Merge pull request #1375 from AnalyticalGraphicsInc/mrt

Multiple Render Targets