Deal with authorship properly, in a future-sustainable fashion

This module is arguably one of the most successful collaborative projects on
CPAN. Make it known to the world by introducing a clear canonical source of
authorship metadata.

I have been holding off jumping on the "contributors from git" bandwagon
because of multiple issues

- Not every contribution results in a direct, attributtable commit
- We already had an extensive contributor list, much larger than the shortlog
- Loss of ircnicks (a fine tradition started in 266bdcc3)

So this commit does the proverbial bullet-biting and introduces *proper*
handling of all the ins and outs, including author-mode (CI as well) tests
for proper attribution. As a side-effect we break a lot of the footer links,
to be fixed in next commit.

Btw as I write this `195 contributors made this library what it is today`...
Mind. Blown.
Clarify licensing, ensure footers are consistent throughout the project

Note - this *DOES NOT CHANGE* the licensing of the project in any way, it
is still dual-licensed like perl5, just as it was before this commit. All
additions are for clarifying purposes only.

The way licensing is presented is an amalgamation of information and
prior art found at the following sources:
 - http://www.perlfoundation.org/cpan_licensing_guidelines
 - https://metacpan.org/source/ETHER/Moose-2.1212/LICENSE
 - `git log --color -w -p v5.20.0 ^perl-5.000^ -- Artistic`