Add support for HTTP PUT and DELETE methods

HTTP PUT and DELETE methods are often used in RESTful APIs. To make
mocking such APIs easier, support for these methods has been added to
MockHttpHandler. For now only RawProtocol with a custom params parser
(e.g. rest_params_parser) can fully handle them, but other protocols may
be updated in the future to allow them too.
Merge pull request #3 from tikan/rest_put_delete

Add support for HTTP PUT and DELETE methods