Attempting to move to using Fog::XML::SAXParserConnection directly
failed because the arguments changed.
This adds another compatibility level with two key differences:
1) It's namespaced within XML so stands out as not being part of core
2) It is NOT creating deprecation warnings so can be used as the final
step if rewriting to use SAXParserConnection is undesired
So when merged Fog::Connection usage will create noise.
Fog::XML::Connection works the same way and will be extracted to
"fog/xml" when we get to it.
Fog::Core::Connection just wraps Excon.request and leaves the response
body parsing to the provider.
