Add amf encoding package, test code

rtmp/amf/decode.go

@@ -0,0 +1,15 @@
+package amf
+
+import "fmt"
+
+type AMFObj map[interface{}]interface{}
+
+func DecodeAMF(data *[]byte) (AMFObj, error) {
+	obj := make(AMFObj)
+	test := make(AMFObj)
+	fmt.Println("a")
+	obj[2] = test
+	fmt.Println(obj)
+	test["tcUrl"] = "test"
+	return obj, nil
+}