Description of Change

Main reason for this PR is to fix a memory leak in queue.h. The changes are similar as in #2235, i.e.:

• std::shared_ptr is used,
• the implementation of queue is const correct,
• std::invalid_argument is thrown when trying to remove/access an element in empty queue,
• queue.h was renamed to queue.hpp,
• proper tests were added (the old file was removed).

Furthermore:

• some typos were fixed,
• The Node class and related utilities have their own file .

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes:
Fixes the memory leak in queue.h