Adopt the BSD 3-Clause License

[Zeitsperre]

FYI @saschahofmann

Following from #12, I would like to propose that lmoments3 adopt the BSD 3-Clause License.

Why?

Most projects started at Ouranosinc are using the Apache v2.0 License, largely because we sometimes integrate logos into the documentation of our projects that are either owned by us or our development partners. This license works well because it's permissive enough to be compatible with downstream open source projects, and it's elaborate enough to satisfy the legal requirements of our non-profit organization.

The text of the Apache v2.0 is really long though, and for lmoments3, this license is overkill. Having something short, concise, and (most importantly) permissive should be the goal.

Why BSD?

Apache v2.0 was developed from the BSD License and, like most open (non-GPL) licenses, is compatible with BSD Licensing. It's short and remains in (IMO) the spirit of the open source licensing intentions for lmoments3 (that it should be widely-used) while also giving credit where due.

Why BSD 3-Clause?

Text of License

The third clause is what's most important to the @Ouranosinc group: We want people building on our software, but we don't want to be labelled as endorsing projects built on our software without our OK. Having that out there is non-negotiable (I imagine others agree).

Assuming we move forward with changing the license, we can migrate the names of all existing copyright owners into the top-matter of the BSD License without issue.