Initial merge of develop branch for Boost 1.74 release

From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2020-07-11 18:31:26

Folks,

I have managed to squeeze the merge of develop into master
shortly before the master is closing for beta later today.

Here is the merge commit:
https://github.com/boostorg/gil/commit/0ac2e42376af142227182135f355025d21a3ebce

Here are notes of changes to be released with 1.74
https://github.com/boostorg/gil/blob/0ac2e42376af142227182135f355025d21a3ebce/RELEASES.md

On behalf of Boost.GIL maintainers, I'd like to send out big thanks to
Samuel Debionne
Pranam Lashkari
Debabrata Mandal
and everyone who participated in discussing or reviewing PRs.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net