Refactor `p_gpg_list_keys`
Add `/pgp autoimport` command,
it's not described in XEP-0027, but used in some clients,
such as PSI, Pidgin. It will autoimport keys received with
`/pgp sendpub`, in plain text as a message, or using features,
provided in other clients. It doesn't autoassign them, but shows
command to assign, letting user to decide.
Improve documentation for some preexisting functions
Add contact argument to `/pgp sendpub`
Command allows to share your PGP pub key with ease,
it's not described in XEP-0027, but used in some clients,
such as PSI, Pidgin.
Fix typos
Minor improvements
