Add tests; only tests the off parser

Test if the order of the vertices is retained. Test that for each facet
the vertex ID is in the same range as the number of vertex ID's
currently available.
Create a package halfedge_mesh

Config.py has a EPISON macro. In order to run py.test you need to run
'pip install -e .' then you can run 'py.test' at the top level
directory.