new overloads return non const iterator

concurrent_map: implement lower and lower_eq methods

Add missing packages in CentOS

docker: fix directory name used in run-doc-update.sh

doc: fix doxygen comments for string_view

basic_string: fix description of allocate method

- correction of documentation
- argument name change to be more human readable

segment_vector: message fix and tests for relational operators

Add tests to check throwing an exception for relational operators

Change copy-pasted error messages to be appropriate.

heterogenerous methods for radix_tree

inline_string: API extension

- modify existing inline_string to check new API

- add two string methods

run coverage job on GHA

cleanup in docker scripts after latest doc job changes

Add conversion operator to basic_string

inline_string reimplementation

Add case to cover conversion operator

Implement conversion operator from string to string_view

- change implementation to template
- move functions definitions outside class

remove doubled clang-format configuration's rule

minor comments updates