Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Improve the INDEX format. Whitespace improvements, format improvements, typo
and grammatical fixes.

Import bsdconfig(8) as a replacement for the post-install abilities of
deprecated sysinstall(8). NOTE: WITH_BSDCONFIG is currently required.

Submitted by: Devin Teske (dteske), Ron McDowell <rcm@fuzzwad.org>
Reviewed by: Ron McDowell <rcm@fuzzwad.org>
Approved by: Ed Maste (emaste)