More comment warning suppressions
Fix tests which need to factor in SemVer

I don't plan on using crazy semver pre-release versions yet so I made
the regex very simple.
Fix warning in XmlAttributeDeserializer
Fix bad matching xml tag
Fix broken unit test

If the response is a bad request, we should probably not have anything
in the request message.
Treat warnings as errors

C'mon! This ain't no amateur hour! :trollface:
Merge pull request #419 from restsharp/more-cleanup

More cleanup