Replace SimplexNoise license link with CC0 instead of Unlicense

[ShirleyNekoDev]

The linked source code did not state Unlicense, but is released as public domain software. While I do not know the legal aspects in detail, I'll assume that CC0 is a better description of the library author's intents.
also see https://chrismorgan.info/blog/unlicense/

[jackjt8]

Looking at the project readme the code was taken from clearly states the license is Unlicense.

Code: Unlicense - You can use it for whatever you want.

https://github.com/keijiro/sketches2016/tree/master

[ShirleyNekoDev]

Oh, you are right. I took the licensing statement information from the file itself SimplexNoise (which is the only part we use), isolated from the repository. Not sure if this would count as separately licensed.

[jackjt8]

public domain software
.
See the GNU General Public License for more details.
.

This is a deeper rabbit hole than I thought. We might need to track back to the original piece of code from ~2011. Depending on the license of that it may overrule any derivatives... Either way this is a bit of a mess.

[ShirleyNekoDev]

See the GNU General Public License for more details.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.

I believe this statement is for details on warranty stuff without having impact on the code license.

Otherwise, there is an email given in the code, which we could contact if needed :)

[jackjt8]

After reviewing the original code there is no mention of GNU. That appears to be an addition made by someone else. The original code is public domain. It's not got a well known waiver or licence, but it's still public domain. As our implementation is based off a derivative work we should maintain the license presented (Unlicense).

Otherwise.. we could always readapt things from the original public domain code. That would solve our license concerns.

[leMaik]

We could as well not mention the license name and just link to the code we adapted.

[leMaik]

The Java port we link to is licensed under the unlicense. It is a port of public domain code.