Use Pod::Usage and begin to develop internal documentation in Perl POD

Use Pod::Usage and begin to develop internal documentation in Perl POD

POD is Perl's native documentation format, designed to embed an
approximate equivalent to a man page inside a Perl program or module.
POD can be particularly useful for docstring-like embedded per-function
documentation but has a different purpose from Texinfo, which will be
used when a reference manual is written.