Adding regular expression matching http header implementation to allow request patterns to specify regular expressions in the header value.  See RegexMatchingHttpHeader.
This changed HttpHeader to an interface as such this will break existing code since they cannot be new'ed up;  use DefaultHttpHeader instead.
Support Regular Expression matching request bodies.  De-duplicate serialization code by removing old Request/Response marshallers and using Gson Type Adapters.  Remove need for ByteArrayResponsePreset since encoding is now handled by BaseBody which is used by both RequestPattern and ResponsePreset.
Merge pull request #3 from hydra/regexp

Support regular expressions for header values and bodies.