Fix examples tests

transaction: remove unnecessary return

print message only if needed and check whitespace in all tests' common files.

without it will fail. SRC_DIR is set (in cmake) for each test based on test name.

CI: fix var name in build.sh and remove redundant WORKDIR var in gha.yml

Reported by coverity

and minor updates in run-build.sh

Fix doxygen docs

CI: minor fixes in CI and utils scripts

and use them in run-*.sh scripts.

- add missing TIMEOUT setup in other_OSes.yml,
- remove redundant code,
- cleanup comments and vars,
- use github.workspace var to set host workdir,
- get rid of old travis gitignore entry.

example: add radix_tree example with complex value type

Minor fix in feature.md

examples: add simplekv_rebuild_string example

Remake tests dir (part 1)

It uses pmem::obj::string as a value type

excluding some pmreorder tests (framework changes are required for that).

docker: fix packages' test - unshallow repo for git describe to work

Extend compatibility tests

docker: centos-8 powertools repo name changed

it's useful, because it uses shallow version of repo and rolling packages.

with more comments and fix binaries dir path.
Add release step to remind to update compatibility tests with new releases.

cmake: add ROOT_DIR and make use of CURRENT_*_DIR variables

Update CMake and package's version in name

and move this piece of code to a helper function.

Fix coverity issues (not catching exception in dtor)

Bump required version of libpmemobj

Since introducing flat_transactions, 1.9 is needed.