PCBScriber is a printer for the scratch 'n etch method, see
http://reprap.org/wiki/PCBScriber
Commit reviewer Traumflug's note:
- Rebased to current branch 'experimental', which adds
USE_INTERNAL_PULLDOWNS.
- Removed DEFINE_HOMING for now, this part isn't cooked, yet.
For example, it doesn't pass regression tests.
- Thank you very much for the contribution!
Matt Gilbert