Add reverse_string utility function in cliutils namespace

[jamisiveshkumar]

Summary

Added a small utility function reverse_string() under include/cliutils/custom_util.hpp.

Details

• Returns the reversed string of given input.
• This is a minimal code-only addition, no documentation or example.
• Code compiles independently with existing includes.

[phlptp]

can you give some explanation of the value this adds to CLI11, what issue it is solving? Assuming it was needed, it would probably be better to add this to stringTools.hpp rather than adding a new namespace and header file

[jzakrzewski]

I don't think such a thing belongs to this library because it has nothing to do with the command line / program arguments / etc.