Add a license

[theoparis]

Can you please add a license such as MIT since this is a recreation? I was planning on forking this repository but I realized it has no license.

[yangfl]

This is way more than a "recreation"... you know what I mean. If you want to reuse these codes just copy them and pretend them as your own work.

If you really care about license stuffs I'd recommend you to rewrite it with PROTOCOL.md.