Added MCNP PTRAC readout support.

Added a class to read MCNP PTRAC files, and a shell script to easily
dump a whole PTRAC file into a HDF5 table.
2 Bugfixes in PtracReader

PtracReader now extends object, and its constructor opens the proper
file.
Merge remote-tracking branch 'upstream/staging' into staging
Bugfixes and test cases for MCNP PtracReader
Fixed PtracReader, added tests for 8 byte MCNP
Switched ptrac script to argparse

(with an implementation of argparse included as a Python < 2.7 fallback)
Merge branch 'staging' of github.com:cbrachem/pyne into cbrachem-staging
some cleanup for ptrac_to_hdf5