Clarify license as BSD 3-Clause License

[justinmayer]

I followed the process for adding a license to an existing repository, and then I copied and pasted the license that GitHub generates for the BSD 3-Clause License type into the existing LICENSE file.

Other than the removal of the "All rights reserved" line, the rest should mostly be formatting changes.

Resolves #284

[Teemu]

Sorry to be pedantic but this includes changes that are not just formatting.

"IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE" turns into "IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE"

[justinmayer]

No need to be sorry — I don’t think you are being pedantic.

But now it is my turn to actually be pedantic: I said that the rest should mostly be formatting changes. 😉

I am aware of this other, very minor addition. An addition that was not made by me, mind you — all the changes here were entirely copy-pasted from GitHub's license generation tool, as noted in the PR description.

Moreover, the text in this PR is exactly — verbatim — what appears in the BSD 3-Clause License. If we do not use the exact same language, then it is not really the same license, which relates to the issue @mociepka originally raised.

Finally, wouldn’t we want to extend the same release from liability to folks who graciously volunteer to contribute to the project?

[justinmayer]

Hey Teemu. Is it okay if we proceed and merge this PR?

[auvipy]

Merging the change as it reflects the current maintainers/contributors as well