GitLab

* Added additional OpenGL error checks
* OpenGL error checks are better usable with namespaces
* Removed checks for OpenGL objects == 0 which would get ignored by OpenGL anyway and are rare
* Added comments
* improved OpenGL ES compatibility

Changed makefile to inlcude the headers and that acgl will automatically build all libraries by default.

shader attributes are now bound by their occurence in the shader source (just before linking the program)