Convert metalN to mN.
Generalize helper constants in modules for
space, width, enclose, etc.
Use layer stacks whever possible.
Try to remove drc() calls in liu of helper constants.
Modify bitcell logic to guess if bitcell is not "bitcell"
No longer need to specify replica (and dummy) bitcell explicitly
Add support for 1 or 2 port replica array.