* Move callback function in thread_pool ctor
* Added const qualifiers to logger.h
* Remove unused includes from file_helper-inl.h
* Fix comments and remove unused include from helpers-inl.h
* Fix typo in comment for set_default_logger method.
* Use `std::move` for `old_logger` in `set_default_logger`.
* Use std::move in example
* Wrap `main` content in try block for exception safety.
* Added coverity to ci