Clean up and generalize layer rules.

Convert metalN to mN.
Generalize helper constants in modules for
space, width, enclose, etc.
Use layer stacks whever possible.
Try to remove drc() calls in liu of helper constants.

compiler/modules/dummy_array.py

@@ -122,7 +122,7 @@ class dummy_array(design.design):
             for cell_column in column_list:
                 bl_pin = self.cell_inst[0,col].get_pin(cell_column)
                 self.add_layout_pin(text=cell_column+"_{0}".format(col),
-                                    layer="metal2",
+                                    layer="m2",
                                     offset=bl_pin.ll(),
                                     width=bl_pin.width(),
                                     height=self.height)
@@ -131,7 +131,7 @@ class dummy_array(design.design):
             for cell_row in row_list:
                 wl_pin = self.cell_inst[row,0].get_pin(cell_row)
                 self.add_layout_pin(text=cell_row+"_{0}".format(row),
-                                    layer="metal1",
+                                    layer="m1",
                                     offset=wl_pin.ll(),
                                     width=self.width,
                                     height=wl_pin.height())