Add a license

[Siphalor]

Currently, this library has no explicit license, resulting in a strong copyright.

As you're welcoming contributions in the README, I suspect this to be an oversight.

You can check https://choosealicense.com/ for a simple overview over some free licenses.

Personally, I prefer using the MIT or Apache 2.0 licenses, but the final choice is up to you (and probably partially me because I contributed without noticing it and therefore probably have copyright on my stuff ^^ - but I'll go with any free license).

[zyansheep]

I defined the license in the Cargo.toml file
license = "MIT OR Apache-2.0"
But I suppose that is probably not standard, I shall make sure to pick a license through github.

[zyansheep]

Okay, I changed the license to the Unlicense License because public domain is cool.