pcb-rnd 3.1.5
~~~~~~~~~~~~~

This release adds minor features and fixes a bunch of bugs.
Change highlights:

1. CAM export: default pnp (pick-and-place) doc export jobs to ps and gerber

2. RefdesText() action and menu, shorthand for creating refdes floater text
   object for subcircuits

3. optional auto-generated pick-and-place helper layer

4. centerline draw export in the HP-GL (plotter) format
