Remove XML and JSON modules

We can move Fog::XML and Fog::JSON to their own gems and providers can
depend on whichever of the two (or both) that they require.

This allows `core` tests to pass but does not account for any untested
cases.
Remove additional parser (XML) code

Few more "core" classes only dealt with XML parsing so are not really
core. The deprecated connection was a layer of insulation between XML
and the Excon connections which can remain in `fog`
Merge pull request #3 from tokengeek/remove_parsing_modules

Remove XML and JSON modules