Add test for facet.halfedges; change id to index
-(untested) Add test; Finished algorithm

The complete algorithm was implement but it has not been tested.

TODO:
    * Test all py.test
    * All new unit test to cover new functions
    * Code review
    * Future: add another mesh to test
Fix fixture and most test had issues

@pytest.fixture has the scope parameter instead of the fixture function.
Finish program

I added the remaining forthe main function in parse_build_halfedge_off
and kept the edges dictionary in HalfedgeMesh. Note I might remove
get_halfedge in the future--it seems unneeded due to self.edges.
Simplified __hash__ for Halfedge because when I kepted all the member
variables as part of the hash they popped the stack with an infinite
loop.
Fix comments add index comparison in __eq__ facet

Add link to pseudo code for main algorithm. Fix a comment in
test_halfedgemesh_vertices_are_in_order_... with regards to Vertex(...)
input.
Can now run py.test on home directory

Data files in tests need tests/data/filename.off in order for py.tests
to work correctly when being run in the project directory.
Merge pull request #1 from carlosrojas/parse_off_and_tests

Parse off and tests