Provide an interface around OpenSSL to dynamically load the libraries
and symbols, so that users can distribute a libgit2 library that is not
linked directly against OpenSSL.  This enables users to target multiple
distributions with a single binary.

This mechanism is optional and disabled by default.  Configure cmake
with -DUSE_HTTPS=OpenSSL-Dynamic to use it.

In commit 70a8fc999d (stop using fnmatch (either native or
compat), 2014-02-15), upstream git has switched over all code
from their internal fnmatch copy to its new wildmatch code. We
haven't followed suit, and thus have developed some
incompatibilities in how we match regular expressions.

Import git's wildmatch from v2.22.0 and add a test suite based on
their t3070-wildmatch.sh tests.

Include the SHA1 collision attack detection library from
https://github.com/cr-marcstevens/sha1collisiondetection

Include the copyright notice from the deps/winhttp/ sources.  Move the
LGPL to the bottom of the file (since multiple dependencies are LGPL
licensed) and include the actual copyright notices from the regex sources.

I accidentally wrote a separate priority queue implementation when
I was working on file rename detection as part of the file hash
signature calculation code.  To simplify licensing terms, I just
adapted that to a general purpose priority queue and replace the
old priority queue implementation that was borrowed from elsewhere.

This also removes parts of the COPYING document that no longer
apply to libgit2.

Signed-off-by: schu <schu-github@schulog.org>