Feature: add ssr support (#805)

* Refactor ssr stream cipher to expose iv and key

References:
https://github.com/Dreamacro/go-shadowsocks2
https://github.com/sh4d0wfiend/go-shadowsocksr2

* Implement ssr obfs

Reference:
https://github.com/mzz2017/shadowsocksR

* Implement ssr protocol

References:
https://github.com/mzz2017/shadowsocksR
https://github.com/shadowsocksRb/shadowsocksr-libev
https://github.com/shadowsocksr-backup/shadowsocksr

component/ssr/obfs/http_post.go

@@ -0,0 +1,9 @@
+package obfs
+
+func init() {
+	register("http_post", newHTTPPost)
+}
+
+func newHTTPPost(b *Base) Obfs {
+	return &httpObfs{Base: b, post: true}
+}