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/protocol/base.go

@@ -0,0 +1,10 @@
+package protocol
+
+// Base information for protocol
+type Base struct {
+	IV       []byte
+	Key      []byte
+	TCPMss   int
+	Overhead int
+	Param    string
+}