Implement Fab exports methods

[rlescanne]

Most of the code is already written in specific files (ask Felix or Ulysse)
We need one method to widden everything on the chip by a small amount usually called overdev
We need another method which takes the negative of a geometry.

[phelyx42]

overdev script: unite the complete metal layer -> copy+move diagonal

xtolerance = pm.set_variable('2um')
ytolerance = pm.set_variable('1um')
gp1 = _chip.copy('gp1')
gp1.translate([xtolerance,ytolerance])
gp2 = _chip.copy('gp2')
gp2.translate([-xtolerance,ytolerance])
gp3 = _chip.copy('gp3')
gp3.translate([xtolerance,-ytolerance])
gp4 = _chip.copy('gp4')
gp4.translate([-xtolerance,-ytolerance])
_chip.unite([gp1, gp2, gp3, gp4])

[phelyx42]

taking the negative is easier

• draw a rectangle with the size of the chip
• subtract metal layer from this rectangle