Merge pull request #27 from pwaller/master

Framebuffer fix for mipmaps
Fix and refactor CaptureToPng(), introduce CaptureRGBA and ClearAlpha
Add Texture.FromImage/png functions
Improve shader API
Merge pull request #30 from pwaller/mrg/texture-enhancements-loading

This adds easy loading of textures.
Merge pull request #31 from pwaller/mrg/shader

Improved shader API
Addresses issue #28. Remove references to `glIndexPointer` and
`gl.EnableClientState(gl.INDEX_ARRAY)` as these prove to be
problematic and entirely pointless.
Whitespace
Fix for #32 - multiple meshbuffers now work