Add Excellon support
Merge pull request #3 from hamiltonkibbe/excellon_support

Add Excellon support
Add setuptools support
Fix parsing of Unknown statements
Fix parsing of COORD with +000 styled numbers
Fix parsing when x or y coordinate is missing on COORD statement
Fix coordinate computation when x or y is 0 in non standard way
Support for zero size C apertures and fix parsing of ADDNN<macro-name>
Merge changes from upstream