Medium-Large release containing 200 commits, bugfixes, enhancements

It's been ~2 years since the last release, so this has quite a few changes. Some highlights:

• Build optimizations and updates. Now needs at least Meson 0.50.0, bot support for VS 2013 dropped in favor of VS 2017 (#952, #955, #934, #933, #932, #911, #883, many others...).
• Lots of bug fixes (incl. #902, #872, #869,
• Lots of enhancements (#873, #
• Lots of cleanup (#870, #867, #865, #864, #847, #849, ...)

Mostly minor bug fixes and improvements, not too many big changes--not ready for version 2.0.0 release yet.