Merge stable-1.9 into stable-1.10

CI: use special environment var in GHA for Windows' PATH

The old 'addPath' is depreciated now. For more details see:
https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

tests: fix parallel_exec_with sync implementation

Since std::condition_variable::wait can wakeup spuriosly we need to
pass a predicate to wait.

Merge stable-1.9 into stable-1.10

Merge stable-1.8 into stable-1.9

Merge stable 1.7 into stable 1.8

Merge stable-1.6 into stable-1.7

docker: make build- and push-image scripts more verbose

Merge stable-1.5 into stable-1.6

otherwise it will still use found (most likely, newer) clang-format.

Update doxygen settings

concurrent_hash_map: make double to size_t cast explicit in defragment()

bump docker images versions

and set clang-format to fixed version (6.0).

and make sure only indexes up to max_index are used.

fixes #854

Merge stable 1.9 into stable 1.10

get rid of old WA for vcpkg and use latest release instead

force removal of docs' dir since it might not exist yet