Initial commit 2021. Opencv 4.2 and bgs 3.0 + added changes from Thomas' bgs-library-fork [WIP not buildable yet]

> forked/mirrored repo @ commit 4e47342e from bgslibrary (just after tag "v3.0")
> added changed Files from bgs-library-fork

see:
git@github.com:andrewssobral/bgslibrary.git
git@gitlab.idiv.de:tb55xemi/bgs-library-fork.git