PEP8ifying.
Moved MeshTally class to mcnp.py. Created Stat_Mesh class.
More improvements to Meshtal and MeshTally classes.
Began adding tests for Meshtal, Meshtally
Added tests and documentation
PEP8ification.
Made suggestions from PR.
Initial work on StatMesh class.
Merge pull request #147 from elliottbiondo/mesh

Meshtal, MeshTally, and outline of StatMesh classes.