doc/neomuttrc.man.head: Sort commands

doc/neomuttrc.man.head: Sort commands

Sorting based on (but not entirely) generated manual.xml file.
Current exceptions are:

  • append-hook, close-hook and open-hook
  • fcc-hook, save-hook and fcc-save-hook
  • lists, unlists, subscribe and unsubscribe

because they are contextually-related commands and therefore grouped and
described together.

Further changes (consistency/readability):

  • macro .TP replaced with .PP or .IP (normal/indented paragraph)
  • command definition(s) enclosed with .nf and .fi (Nofill/Fill mode)