Create a BaseGLProxy class in gloo/gl/_proxy.py

This class is autogenerated and can be subclassed for different
purposes, such as a main proxy, a debug proxy, webgl or IPython
backend, etc.

By putting the functions in a class, a new set of functions can
be easily "created" simply by instantiating the class. The functions
all use __call__ to "serialize" the API calls. Subclasses can thus
simply implement __call__ in the appropriate way.
gl api does not have kwargs
Add stub webgl backend.

This should get whomever is going to work on the webgl
backend started.
GL proxy class derives from object.

Also fixed that __call__ does not have kwargs in base class.
Merge pull request #202 from almarklein/gl-proxy-class

Gl proxy class