Description of Change

Since the input size of postfix_evaluation is a template parameter, this function needs to be compile for every used input size (this increases both the build time and the size of the binary).

This PR changes the the type of the input to std::vector to avoid such problem.

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:
Use std::vector as input type, to avoid increase of build time and binary size.