Improve 'help' command
POD documentation has been modified to list available shell commands using =head2
instead of =item.
This, combined with run_help() modified to accept arguments, allows one to use
'help <command name>' to get help for a specific command, similar/equal to getting
help for shell builtins in regular shells.
E.g.:
help cat
help list
Adam Spiers <adam@spiers.net>
Andr Goens <andres.goens@tu-dresden.de>
Alexander Perlis <aperlis@math.lsu.edu>
Dennis Kaarsemaker <dennis.kaarsemaker@booking.com>
Emile "iMil" Heitor <imil@home.imil.net>
Gertjan Halkes <shelldap@ghalkes.nl>
Giacomo Tenaglia <Giacomo.Tenaglia@cern.ch>
Jonathan Rozes <jonathan@laika.com>
Josef Wells <Josefwells@alumni.utexas.net>
Landry Breuil <landry@openbsd.org>
Lars Täuber <taeuber@bbaw.de>
Michael Granger <ged@faeriemud.org>
Michael Raitza <spacefrogg-devel@meterriblecrew.net>
Mike Hix <m@hix.io>
Peter Marschall <peter@adpm.de>
Rick H. <rickh_shelldap@printstring.com>
Rong-En Fan <rafan@FreeBSD.org>
Salvatore Bonaccorso <carnil@debian.org>
Yann Cezard <yann.cezard@univ-pau.fr>