Use packages for imports.

Must set PYTHONPATH to include OPENRAM_HOME now.
Reorganizes subdirs as packages.
Rewrites unit tests to use packages.
Update README.md with instructions, dependencies etc.
Update sky130 module imports.
Change tech specific package from modules to custom.

compiler/modules/write_driver_array.py

@@ -5,16 +5,16 @@
 # (acting for and on behalf of Oklahoma State University)
 # All rights reserved.
 #
-import design
+from base import design
 import debug
 import math
 from tech import drc
 from sram_factory import factory
-from vector import vector
+from base import vector
 from globals import OPTS
 
 
-class write_driver_array(design.design):
+class write_driver_array(design):
     """
     Array of tristate drivers to write to the bitlines through the column mux.
     Dynamically generated write driver array of all bitlines.