bindAttribLocation with matrix attributes

This test verifies that vectors placed via bindAttribLocation right after matricies will fail if there is insufficient room for the matrix.
Merge pull request #699 from RafaelCintron/bindAttribLocationMatrix

bindAttribLocation with matrix attributes
Added extension annotations describing compatibility across spec versions
Merge pull request #700 from toji/extension_versions

Added extension annotations describing compatibility across spec versions
Add information on planned backwards incompatibility in WebGL 2

It was decided in the WebGL WG F2F that WebGL 2 will not be entirely
backwards compatible with WebGL 1. In particular, there is agreement
that all extensions are not moving over, and always enabling primitive
restart in WebGL 2 significantly streamlines implementations, so that
could be added to this section of the spec.
Merge pull request #701 from NVIDIA/webgl2-backwards-compatibility

Add information on planned backwards incompatibility in WebGL 2