Python API: Add enum and union support.

As well as a rewrite of the encoders/decoders to make it more readable and extensible.
(Re-commit after fix to verify build.)

Change-Id: Ic244d3cebe070bb2570491f8a24f4a1e203f889a
Signed-off-by: Ole Troan <ot@cisco.com>

test/vpp_papi_provider.py

@@ -70,7 +70,7 @@ class VppPapiProvider(object):
             for filename in fnmatch.filter(filenames, '*.api.json'):
                 jsonfiles.append(os.path.join(root, filename))
 
-        self.vpp = VPP(jsonfiles, logger=test_class.logger)
+        self.vpp = VPP(jsonfiles, logger=test_class.logger, read_timeout=5)
         self._events = deque()
 
     def __enter__(self):