Mbtest

* HTTPS support.

* Bugfix - Stub.from_structure() decodes logically combinable predicates. (Thanks, [SShatun](https://github.com/SShatun).)

* Add support for PATCH HTTP verb. (Thanks to [garry-jeromson](https://github.com/garry-jeromson).)
* Add NotPredicate.

* Bugfix - Ensure imposter host matches server host

* Add [dynamic predicates and responses](http://www.mbtest.org/docs/api/injection). This feature requires Mountebank 2.0 or later, but all other features should continue to work with older version.
* Add MountebankServer.query_all_imposters() method to retrieve all imposters from a running MB server, including those not created locally.

* Allow MountebankServer to attach to an already running MB instance on another host.
* Make has_request() a builder style matcher, and use builder matcher construction wherever possible.