obfs4proxy is a Tor pluggable transport proxy, implementing obfs4.

This commit also includes obfs4proxy's build time dependencies:

* golang-github-agl-ed25519: Go implementation of Ed25519 signature
  algorithm
* golang-github-dchest-siphash: Go implementation of SipHash-2-4
* golang-golang-x-crypto: Go supplementary cryptography libraries
* golang-golang-x-net: Go supplementary network libraries
* golang-golang-x-sys: Go packages for interaction with the OS
* golang-golang-x-text: Go text processing support
* golang-torproject-pluggable-transports-goptlib: Tor pluggable
  transports library for Go

Signed-off-by: Jeffery To <jeffery.to@gmail.com>