Layer: Add class documentation and remove ::create()

	* Add class documentation.
	* Remove ::create() method as Layer is an abstract type.
Renderer: Wrap ChamplainRenderer
MapSource: Cleanup

	* Remove no longer existing properties.
	* Add vfuncs.
	* Reorder methods.
Fix global include file champlainmm/champlainmm.h

Replace old directory structure (libchamplainmm/) with new one
(champlainmm/) in champlainmm/champlainmm.h