Cleaned up --help output, expanded manpage

(I noticed the -p flag wasn't documented in the manpage, or listed in the command usage synopsis, so I added it. While I was in there I also did some expansion and cleanup; no changes to functionality.)

* Options list in --help output sorted into natural/priority order
* -p flag added to --help synopsis, documented in manpage
* Manpage SYNOPSIS section formatting is now more robust/canonical
* Ordered usage, options list in manpage to match --help message
* Added EXAMPLES from README.md to man page
* Minor copyediting/expansion of documentation and help