Integrate wormhole-client repo into this repository

[vu3rdd]

Right now, this repository implements the core magic-wormhole protocol and the wormhole-client repository implements the file transfer protocol and a client executable that is compatible with the canonical Python magic-wormhole implementation. In the future, we may want to implement dilation and other ideas too. It would be best to do it all in one repository and split into two. So, we will slowly integrate the code in wormhole-client repo into this repository. I don't know how we would do that in a history preserving way. May be we would just archive the other repository and make it read-only. Any other ideas welcome.