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/wordline_buffer_array.py

@@ -6,21 +6,21 @@
 # All rights reserved.
 #
 import debug
-import design
+from base import design
 from tech import layer
-from vector import vector
+from base import vector
 from sram_factory import factory
 from globals import OPTS
 from tech import layer_properties as layer_props
 
 
-class wordline_buffer_array(design.design):
+class wordline_buffer_array(design):
     """
     Creates a Wordline Buffer/Inverter array
     """
 
     def __init__(self, name, rows, cols):
-        design.design.__init__(self, name)
+        design.__init__(self, name)
         debug.info(1, "Creating {0}".format(self.name))
         self.add_comment("rows: {0} cols: {1}".format(rows, cols))