Implement SOCKS4/4a/5 client

[anonimal]

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Mentioned in #149, we should have a client option to tunnel reseed requests through a SOCKS server. Ideally, we have a SOCKS client that tunnels whatever we want through the server; e.g. all traffic or just NTCP when we implement 'hidden mode/disabled inbound/disabled UDP'.

Non-Tor PT implementation has been discussed in the past but, for the time being, a simple SOCKS client would be of great service; especially for obfsproxy users or anyone who wants to reseed through Tor.

Boost has a classic SOCKS4 client example available and making it 4a would not take much work. SOCKS5 on the other hand will take a little more work; at least to do well. We have a SOCKS server that looks mostly functional and at first glance appears to adhere to spec (but no guarantees) should anyone wish to look at a server implementation for client-related material.

Whether this SOCKS4/4a/5 client is available in libcore and/or libclient is up for debate.

[anonimal]

In today's meeting, it was agreed to keep this only in client.

[anonimal]

NOTICE: THIS ISSUE HAS BEEN MOVED TO GitLab. Please continue the discussion there. See #1013 for details.