RexPro Authentication Fixed

Problem seemed to stem from the "Empty" session default of `None` serializes to \xc0, whereas the spec dictates a byte(16) of \x00

Also Includes:
  - Testing suite updates
  - Requirements updates
  - Coverage script
  - Setup.py updates
  - Python 2 & 3 compatibility -- needs testing - known to work with Python 2.7.5+ - Tox included for testing 2.7.5, 3.2, 3.3
  - Improved code coverage
  - PEP8 and formatting