Adds python interface with interrupt fixes

These commits add two features and fix one issue:
  Features:
    1.  Adds a version query interface so that the user can see the PRUSS version
    2.  Adds a python interface to the prussdrv library.  This interface includes a base class for a python compatible interrupt handler (generally, pthread approach used in the c-library is not possible with python because of the global interpreter lock (GIL)).

  Fix:
    As indicated by others already, there is an issue with interrupts being retriggered in the original prussdrv library.  This corrects that issue and also makes the event/channel/interrupt nomenclature a bit more clear.