Add support for TF command (FileAttribute) from GerberX2

[shane-circuithub]

[shane-circuithub]

This is completely untested right now, but I'm interested to see if either of you have any comments on the work so far before I go any further with it.

[HanStolpo]

I see we don't have a printGerber to go with the parseGerber, so ignore my comment about a round trip test, we should probably add that in a future enhancement, especially when we want to convert Excellon Drill files to Gerber X2 files at a later stage.

[ocharles]

I see we don't have a printGerber to go with the parseGerber, so ignore my comment about a round trip test, we should probably add that in a future enhancement, especially when we want to convert Excellon Drill files to Gerber X2 files at a later stage.

I wouldn't ignore this comment, it's a fundamental architectural choice of the parser to try and faithfully parse the input into a data structure as close as possible to the input.