License for RFCs

I propose establishing a license for Haxe RFCs, just like other languages or specifications.

I suggest using:

- CC-BY 4.0
- MIT

Since an RFC can contain code samples, you can use CC-BY for the content, MIT for the code samples, CC-BY and MIT for both (dual licensing), or use MIT for the entire RFC at all. A popular strategy in documentation (e.g. MDN) is to license the content and public domain for the code samples (i.e. CC-BY + CC0).

Another option is to adopt CC0 for everything, just as Python adopted the public domain for PEP.