Add shadowtls (#49)

* Add shadowtls outbound

* Add shadowtls inbound

* Add shadowtls example

* Add shadowtls documentation

option/shadowtls.go

@@ -0,0 +1,17 @@
+package option
+
+type ShadowTLSInboundOptions struct {
+	ListenOptions
+	Handshake ShadowTLSHandshakeOptions `json:"handshake"`
+}
+
+type ShadowTLSHandshakeOptions struct {
+	ServerOptions
+	DialerOptions
+}
+
+type ShadowTLSOutboundOptions struct {
+	OutboundDialerOptions
+	ServerOptions
+	TLS *OutboundTLSOptions `json:"tls,omitempty"`
+}