Can now execute arbitrary HTTP methods (such as "copy" or "move") using
get- or post-style request semantics. Added sync and async support for
both. Refactored a bit of RestClient.Sync and RestClient.Async to
If a user overrides the IHttpFactory, RestCLient shouldn't overwrite the
default user agent with its own unless both the RestClient and the Http
instance both have not set the user agent to a proper value.