Gloo

### New GLOO API

This is the (final ?) PR for the new gloo API. It is not yet finished and tested but we might want to merge it anyway since it is blocking other PR.

If you feel it needs more work, just le me know (I might not be able to work on it this week).

I still need to take Almar's comment + new GL backend into account, fix some of the examples and write a proper documentation through the tutorial.

Next step for gloo would be to reorganize examples (#104) and handle issues #114, #120, #149 & #150.

Then I can move on to handling GLSL > 3.0 shader syntax to check if this can be unified through gloo.