recommit: Add DebugServerClient class to communicate with debugserver

Previous pull request are [here](https://github.com/libimobiledevice/libimobiledevice/pull/158), I follow your instructions modified it:

### Changes

* Use real name "Hao Zhou" in git commits
* Split mobile_image_mounter changes into [05fa8d0](https://github.com/upbit/libimobiledevice/commit/05fa8d0a048cc92048a03eb06dd8883f9c76a632)
* Removed "TO-DO" and handle_response() method in debugserver.pxi

Thank you for taking the time to review the code.