Account for piercing and torch width

[dbenamy]

See if anything in the toolchain can deal with this for us. If not, check out http://opensourceecology.org/wiki/DXF_to_G-code_Conversion_Tutorial#Piercing

The "torch" should move back and forth while making an initial "pierce". For the circle, I think it should make the pieces inside the circle. I'm not sure if it should pierce the rectangle inside or on one edge. We want it to make the pierce in a part of the metal we won't use. I wonder how the piercing code knows what that is... There's a conversation at https://groups.google.com/forum/#!msg/dxf2gcode-dev/6ZnNcX3O5i4/d-3NeBfHpbUJ about integrating this functionality into dxf2gcode which would be great for ease of use and gives us a gui where maybe we could click where we want the pierce to be.

[dbenamy]

For milestone 1 (cutting real plates), I'm hand writing gcode so I'll take this into account.

This really needs to get dealt with when we get dxf to gcode going (#19).