Added function concrete.util.generate_UUID()
Fixed function concrete.util.generate_UUID()
Fixed another import issue with concrete.util.generate_UUID()
Added function concrete.util.write_communication_to_file()
Added example script showing how to create a Communication
Removed global variable
When testing if a word is in the dictionary, now using lowercased word
Added doc strings to functions
Copied functions from concrete.util for reference
Error handling for concrete_type is now handled by argparse.

The concrete_type command line option specifies the type of Concrete
object to convert to JSON.  There is a whitelist of possible types,
and the two current options are 'communication' and 'tokenlattice'.
The script was using some custom code to check if the value for
'concrete_type' was on the whitelist, but this checking is now handled
by argparse.
Made 'concrete_type' an optional parameter instead of required
Added a main() function to test_uuid.py
Added utility function to create references for each UUID 'pointer'

The Concrete schema uses UUIDs as internal pointers between Concrete
objects.  The add_references_to_communication() adds member variables
to Concrete objects that link to the Concrete objects pointed to by
the UUIDs.
Fixed bug in add_references_to_communication()
Fixed another bug in add_references_to_communication()
Validation code now checks TokenRefSequence token indices
Fixed bug in TokenRefSequence validation code