Fix #308

[hildogjr]

@quick, this may need some check:

1. if I merged something wrong by using the KiCad plugin repository code as base for my fix;
2. if the pcbdata["metadata"]["outputfolder"] data that I create broke the other EDA that your plugin works with).

[qu1ck]

There are few problems here

1. Definitely needs to be rebased on top of master
2. This is kicad specific. Doesn't work at all for other supported EDAs and this should be mentioned in the substitutions tip text.
3. This will crash for other EDAs because you are accessing board object of the parser which doesn't exist in other parsers. Move that logic into kicad.py and do %o substitution only if the field exists in metadata.

[qu1ck]

Closing as the issues I mentioned above have not been fixed for a year.