Add thread

Will replace #28.

Waiting for https://github.com/cinemast/libjson-rpc-cpp/pull/56.
Look at the commit message ;) https://github.com/MiLk/mage-sdk-cpp/commit/d9049d3a150b1814fa1cb87b3253e82983f1c826

It's for https://github.com/cinemast/libjson-rpc-cpp/pull/56