Add KHR_debug definitions
Load KHR_debug on Linux
Fix import problem
Define GL callback func. Improve GL err macro.
Implement debug callback
Enable all messages
Improve formatting
Stop mipmap allocation for textures
Add GL_ARB_debug_output
Add debug markers and labels
Fix iOS compile
move pixel flip from headless test into HeadlessView::readPixels
fix memcpy includes/namespace
Merge pull request #673 from mapbox/pixel-flip

Move pixel flip from headless test into HeadlessView::readPixels
Merge pull request #670 from mapbox/gl-debug

Use GL debug callbacks
update nunicode version to 1.5.1
untabify
More complete uv::thread
Adhere to naming conventions
Texturepool ⇢ TexturePool (fixes #655)