pyloxi: Connection class

This class creates a thread which continually parses OpenFlow messages off the
supplied socket and places them in a queue. The class has methods for reading messages
from the RX queue, sending messages, and higher level operations like request-response
and multipart transactions.

I'm putting this in Loxigen because it's so commonly used even though it goes
beyond the usual LOXI scope of serialization.
diff --git a/py_gen/codegen.py b/py_gen/codegen.py
index 9c741d2..aa7141a 100644
--- a/py_gen/codegen.py
+++ b/py_gen/codegen.py
@@ -88,6 +88,7 @@
     render('__init__.py', template_name='toplevel_init.py')
     render('pp.py')
     render('generic_util.py')
+    render('connection.py')
 
     for version in loxi_globals.OFVersions.all_supported:
         subdir = 'of' + version.version.replace('.', '')