Give the Go pluggable transports library its own home
The library that currently lives at https://gitweb.torproject.org/flashproxy.git/tree/HEAD:/websocket-transport/src/pt is nice, and is already being used by a separate program, the super-proxy server in #7167 (moved). It should have its own home separate from the flashproxy tree, like pyptlib is separate from obfsproxy.