Split proxy off into its own repository

[nyonson]

It was a bit awkward having a binary in the workspace. Binaries want specific versions for dependencies, whereas libraries work on ranges of dependency constraints. Splitting it off to simplify the dependency tree.

First patch fixes the bufreader example, not sure how that wasn't causing CI issues before.

[rustaceanrob]

ACK 4693e67

I wonder if worthwhile to check in on btcd and neutrino to see if they have V2 transport. There is also libbitcoin and BitcoinJ. In that case you may want to list a few clients the proxy is compatible for. Perhaps overkill, but maybe you can place it behind a Socks5 proxy so clients don't need to patch existing functionality if they are already using Tor?