Add primitive rendering types

Add primitive rendering types

These types are not full GObjects, hopefully they will be faster and
more space efficient this way since there will likely be a very large
number of these objects. However, the API is similar.

GisProjection:
  Stores camera parameters.

GisPoint:
  Corresponds to OpenGL Vertex.

GisPrimitive:
  Base class for primitive drawing objects.
    - Contains a centroid for depth sorting
    - Contains a projection so that xyz values for vertexes associated with the
      primitive points can be store relative to a projection.

GisTriangle:
  For GL_TRIANGLES

GisQuad:
  For GL_QUADS

GisCallback:
  Contains a callback and user_data pointer that is called when the object is
  to be rendered.