Unlike last attempt this replaces Fog::Connection with
Fog::XML::Connection which should be directly compatible.
Fog::Connection is there for old PRs but should be removed real soon.
Providers using JSON should be able to replace "XML" with "Core" within
their code to cut down on the dependency.
If I get the time I may attempt to clean up some but testing with Mock
will mean that is mostly educated guesswork.
Fog::Connection mixed in XML parsing via the `parser` argument which
wasn't much use for the majority of APIs using JSON.
This adds the deprecation warning and attempts to update providers to
the correct version of Connection that they need.
Either the cleaner `Fog::Core::Connection` or if reliant on the XML
parsing still `Fog::XML::SAXParserConnection`
The SAX parser will be moving to `fog/xml` fairly soon.
