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/tests/10_write_driver_array_test.py

@@ -9,7 +9,7 @@
 import unittest
 from testutils import *
 import sys, os
-sys.path.append(os.getenv("OPENRAM_HOME"))
+
 import globals
 from globals import OPTS
 from sram_factory import factory