Remove multiple context support (remove LoaderExec); Fixes #20
Allow gfx.Color vertex attributes (see azul3d/gfx#12).
Document default shader inputs; Fixes #16
Remove blank trailing comment.
Merge branch 'master' of https://azul3d.org/gfx/gl2.v2 into v3-dev
Merge v3-dev branch into v3-texcoords-colors

I meant to use v3-dev as the base, sorry.