pcb-rnd 1.2.4
~~~~~~~~~~~~~

This release starts the next major undertaking of pcb-rnd: the data
model cleanup. The internal data model has been upgraded into a more
proper tree; subcircuits has been added to group arbitrary objects.

This effort triggered various cleanups and fixes, including a more
coherent model how layers are stored in buffers and subcircuits, enabling
them to be reused among boards with different stackups.

The io_ plugins evolved too: pcb-rnd can read binary board files
produced by eagle and read/write Protel's autotrax/easytrax format.

The xy_ exporter has been upgraded to use templates for its output format.
This enables pcb-rnd to support different fabs easier. Adding support
for a new fab is a question of adding a new template - usually no coding
required.