Command line execution of tool scripts broken due to relative imports

[mpsonntag]

Command line execution of the scripts tools/format_converter.py, tools/xmlparser.py and terminology.py lead to the error:

SystemError: Parent module '' not loaded, cannot perform relative import.

This also affects #122.

[mpsonntag]

All scripts can be run using python -m .... The last problem was solved with PR #342.