Make "usage" messages use the same EBNF as the User's Guide;
no angle brackets.  Improve and correct various helptexts.

Specifically for the port commands, clarify that the number
is optional, and omitting it causes the current number to be
displayed.

Don't use "&function"; a function's name is its address.
Remove a couple instances of pointless whitespace; shrink a
few overlong lines.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>