Implementation of gms functions necessary for get_message

gms.py is a python implementation spiritual successor to libgms. It
contains all the necessary functions to implement get_message
Deprecate the C get_message

The python version (based on gms.py) contains all the necessary
functionality.
Include a main method for get_message
Simplify logic
Rename gms.py to get_message
Ship a setup.py
Update debian packaging for version 10.1
Remove Debian packaging from master