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_mask_and_array.py

@@ -5,15 +5,15 @@
 # (acting for and on behalf of Oklahoma State University)
 # All rights reserved.
 #
-import design
+from base import design
 import debug
 import math
 from sram_factory import factory
-from vector import vector
+from base import vector
 from globals import OPTS
 
 
-class write_mask_and_array(design.design):
+class write_mask_and_array(design):
     """
     Array of AND gates to turn write mask signal on only when w_en is on.
     The write mask AND array goes between the write driver array and the sense amp array.