doc: add examples/ to EXAMPLE_PATH in doxyfile

concurrent_map: fix typo

Without this, doxygen cannot find doc snippets from examples.

added simple example for string

Add missing constructor to concurrent map

Fix clang format lookup

on Ubuntu it's called "clang-format-9" not "...-9.0".

Add missing constructor
Enable compare.pass test

update docker containers version to 1.11

LIBCXX map tests: CONS

Port cons tests taken from libcxx master branch

Remove aliases for reverse iterator from the skip list

License dates fixes

These aliases were added by mistake and do not make sense because the
concurrent skip list supports only forward iteration.

Change of date in licenses

 Generic erase tests enablement

tests: make vector_ctor_exceptions_nopmem test generic

Add helper function to map wrapper
Enable generic erase tests

 Enablement of generic emplace test

So that it can be used to test radix tree

 Enable emplace test
 Add helper classes taken from libcxx

Enable libcxx tests for radix

Add document describing requirements for containers

update RELEASE_STEPS.md

- cleanup what's not needed
- define what $VERSION and $VER mean
- clean up some sentences and add announcements on slack channel

to avoid any conflicts with feature flags (if we ever add them)

Update CI files, incl. coverage-related fixes

now it explicitly says it executes debug job, with
additional COVERAGE variable set.

Change in upstream repo may (and did) break our coverage. It's best to use fixed version,
with a patch applied (incl. removal of an excessive log, due to the log limit in CI).

- exit 1 if not successful
- add prints and update comments
- check for gcov leftovers; codecov's script should parse and remove them

Extend error handling in allocator<void>::allocate