to avoid warnings in build logs.

in run-doc-update.sh created PRs.

and additional minor cleanups in run-doc-update.sh

and don't build docs.

- tidy up workflow files,
- make scripts more verbose,
- unify printed messages,
- use proper ${} bash variables syntax,
- order code,
- remove redundant code.

Merge stable-1.11 into master

modify slice to work with output iterators

radix_tree: fix use after free

Iterator inside erase() cannot be incremented after calling delete_persistent.
Incrementing checks the value of leaf_->parent which means reading from free'd memory.

Merge stable-1.10 into stable-1.11

basic_string: remove workaround to compile under VC++2015

After added conversion operators there is no need
to manually cast string to string_view. Casting in this case
produces VC++2015 errors due to operator==() ambiguity.

Merge stable-1.9 into stable-1.10

docker: add Ubuntu-18.04 docker image and test it in other_OSes.yml

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/

Fix TBB cmake

string_view: VS2015 build fix

- remove class namespaces before class members which
  are in the same namespace to avoid compilation errors

- print more concise messages,
- make it required when TESTS_TBB is on.

string: unify description of find API

- change description to be the same for string and string_view

string_view: move find API implementation from string

- change function body to use conversion operator to string_view and
  call find*/rfind* function accordingly

- add find*, rfind* functions to string_view

Bump OSes versions

Don't use github.repository variable in workflow files

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

Map example fix

So that hashmap is not always empty after reopen.