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/precharge_array.py

@@ -5,14 +5,14 @@
 # (acting for and on behalf of Oklahoma State University)
 # All rights reserved.
 #
-import design
+from base import design
 import debug
-from vector import vector
+from base import vector
 from sram_factory import factory
 from globals import OPTS
 
 
-class precharge_array(design.design):
+class precharge_array(design):
     """
     Dynamically generated precharge array of all bitlines.  Cols is number
     of bit line columns, height is the height of the bit-cell array.