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

adapters/outbound/parser.go

@@ -24,6 +24,13 @@ func ParseProxy(mapping map[string]interface{}) (C.Proxy, error) {
 			break
 		}
 		proxy, err = NewShadowSocks(*ssOption)
+	case "ssr":
+		ssrOption := &ShadowSocksROption{}
+		err = decoder.Decode(mapping, ssrOption)
+		if err != nil {
+			break
+		}
+		proxy, err = NewShadowSocksR(*ssrOption)
 	case "socks5":
 		socksOption := &Socks5Option{}
 		err = decoder.Decode(mapping, socksOption)