Investigate RPi / GL ES 3.0 Support

[ryanisaacg]

Copied from a comment on Quicksilver:

ERROR [golem::shader] Failed to compile vertex shader: 0:1(10): error: GLSL 1.50 is not supported. Supported versions are: 1.10, 1.20, 1.00 ES, and 3.00 ES

Can golem support any of these GL versions? It may be as simple as lowering the emitted GLSL version, but maybe 1.50 was chosen for a reason (I honestly don't remember.)