Implement GLES3 functions:

* glGetActiveUniformBlockName
* glGetActiveUniformBlockiv
* glGetIntegeri_v
* glGetUniformBlockIndex
* glGetUniformIndices
* glUniformBlockBinding
Merge remote-tracking branch 'remotes/djg/webgl2-uniformblock-1' into incoming

Conflicts:
	src/library_gl.js
Merge branch 'djg_gl' into incoming

Conflicts:
	AUTHORS