gloo.gl: rename angle to es2 and implement for Linux
gloo.gl: add dummy backend (each function raises error)

For when the rendering is done elsewhere.

Gloo initialize (for desktop/es2) compat implemented better
gloo.gl handle desktop/es2 compat in GLIR

Compat for initializing point sprites for desktop.
Compat for modifying shading code.
Program can now read variables with precision qualifiers.
Qt now supports EGL on Linux. We can run real ES 2.0!
support for RPI (does not really work yet
deprecate es2 on Windows
Minor simplification in ndscatter example: there's no need to compute the matrix exponential anymore.
Merge pull request #587 from rossant/updated-ndscatter

Minor simplification in ndscatter example
small fix in qt, add test for added code in glir
Merge pull request #593 from almarklein/real-es2

Real es2
Merge remote-tracking branch 'vispy/master' into visuals-layer

Conflicts:
	vispy/app/canvas.py
	vispy/util/config.py