#72 Add py filter to Stepconf

[Phil]

I think this is what is happening, my apologies in advance if I'm doing this incorrectly and this is a bogus request. I manually edited the Stepconf produced .ini file to add a the filter section to use the python G-code generators. Now updating other parameters using Stepconf looses that filter. It would be nice if either Stepconf recognized that type of manual edit and didn't bother it, or it included the capability to add the filter section.