Add a custom protocol over SSH for TCP and UDP communication

[imterah]

Summary

This introduces a new backend (& custom protcol) called sshpy.

[imterah]

Before I merge this, I need to implement these things (afaik):

• I'm using 32 bit numbers for no reason. I should probably switch this to 16 bits, but maybe keep this for the client IDs
• I probably should write documentation on the protocol and the code, since it isn't really off the shelf, and the code is ~1.3k lines so far in total

[valnyx17]

This PR will fix issue #9.