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/origin.go

@@ -0,0 +1,36 @@
+package protocol
+
+type origin struct{ *Base }
+
+func init() {
+	register("origin", newOrigin)
+}
+
+func newOrigin(b *Base) Protocol {
+	return &origin{}
+}
+
+func (o *origin) initForConn(iv []byte) Protocol { return &origin{} }
+
+func (o *origin) GetProtocolOverhead() int {
+	return 0
+}
+
+func (o *origin) SetOverhead(overhead int) {
+}
+
+func (o *origin) Decode(b []byte) ([]byte, int, error) {
+	return b, len(b), nil
+}
+
+func (o *origin) Encode(b []byte) ([]byte, error) {
+	return b, nil
+}
+
+func (o *origin) DecodePacket(b []byte) ([]byte, int, error) {
+	return b, len(b), nil
+}
+
+func (o *origin) EncodePacket(b []byte) ([]byte, error) {
+	return b, nil
+}