Moved primary Excellon-format writing code to excellon.py. The Excellon stuff still needs more refactoring and consolidation.
The tool sizes are now properly written in the Excellon header. Also the toolnames are now properly written in the body of the file.
Fixed debugging output in drillcluster.py. Probably broke when converted to Python3.
Tools are now numbered in order of increasing size. Seems to be good form, or at least a defacto standard for Excellon files. At least it makes it more readable.
The drill file parsing now both runs in Python3 and is correct. Also been refactored to be a little simpler.
Removed reliance on config module from a few aptable.py functions
Removed requirement on config module from aptable.py