Owsmaster

Large pull request... was going to be difficult to pull everything out into separate features

New support:
* Adds SOS support (GetCapabilities, DescribeSensor, GetObservation)
* Adds SensorML support (used in SOS DescribeSensor)

Testing:
* Using py.test for test running (see TESTING.txt for details). Organized tests and testing resources.  All tests are now passing.  When possible the remote resources were localized into XML files.

Other changes:
* The many lists of namespaces throughout were all moved to namespaces.py.  Methods on the OWSLibNamespaces object allow querying namespaces based on acronym and version.
* Ability to parse Crs URIs like: http://www.opengis.net/def/crs/EPSG/0/<EPSG code>
* General cleanup