Large changes to build system, preliminary CGAL support

Moved building of library to CMake with only installation performed by
distutils.  Need to sort out creating standalone libraries.

Added preliminary CGAL support, disable by defining CSG_NO_CGAL.  Seems
to be more stable, however may encounter issues when the CGAL
NEF_Polyhedron_3 instances that are produced are non-simple.  Seems to
pass Dave Curtis' test case, although simple modifications of the
parameters can trigger seg-faults.