Many corrections and updates, mostly from NetBSD, but with some of my very own

Many corrections and updates, mostly from NetBSD, but with some of my very own
special sauce: document the FreeBSD (Fx) and NetBSD (Nx) macros, add the
section 9 "Kernel Manual" to list of man page ``volumes'', mention the two
situations where the `.Nm' macro should always be given an argument, correct
description of -ragged display and add description for -unfilled, note that
-enum lists cannot be nested within themselves or displays, document a couple
more tagged list types, demonstrate that -width is not really optional for -tag
lists, document the -column list type, all kinds of formatting nits repaired,
and a partridge in a pear tree.