moved of_g to c_gen.of_g_legacy, introduced loxi_globals

as of_g includes loads of legacy data (and a representation that
is increasingly tailored to the c backend only), I've moved it to
c_gen.of_g. In its place, I have created loxi_globals, which gives
access to the list of versions and the IR.

Also loxi reorg: move command line processing to cmdline.py
diff --git a/c_gen/c_code_gen.py b/c_gen/c_code_gen.py
index e35ee8d..1106f2d 100644
--- a/c_gen/c_code_gen.py
+++ b/c_gen/c_code_gen.py
@@ -31,7 +31,7 @@
 """
 
 import sys
-import of_g
+import c_gen.of_g_legacy as of_g
 import c_match
 from generic_utils import *
 from c_gen import flags, type_maps, c_type_maps
@@ -40,6 +40,7 @@
 
 import c_gen.identifiers as identifiers
 
+# 'property' is for queues. Could be trouble
 
 ################################################################
 #