Add MIT license to haxelib

[Maniues]

This patch adds MIT license to this repo (as stated in package.json and haxelib.json).

You can modify this license to add to copyright notice other contributors included in haxelib.json.

[Maniues]

@Simn, @andyli, could you merge this? License is the fundamental for contribution in Open Source project.

[Simn]

I have some vague memory of the licensing being a bit more difficult for haxelib in particular, but I don't remember any details.

[Maniues]

@Simn As I said earlier, many Haxe projects have licensing issues (usually there is no LICENSE file in git repo). I wrote an email to the Haxe Foundation once and repeated the issue recently, but never received any response.

As I understand it, these are Open Source projects. All in all, very good and useful. I don't know how it's possible that they have such problems, but I want to help solve them, hence all the PR with adding licenses.

Could you check what the haxelib licensing issues were? The haxelib.json file says "MIT", so I assumed that this license covers this project and it should be there, but I don't think it would be bad if it was a mix of e.g. Apache-MIT or just GPL or something similar.

[Simn]

Ah okay, if the haxelib.json already says it then I guess somebody has thought about it before.

[Maniues]

@Simn maybe you meant this #535