Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

jail(3lua): add a jail.list() method

This is implemented as an iterator, reusing parts of the earlier logic
to populate jailparams from a passed in table.

The user may request any number of parameters to pull in while we're
searching, but we'll force jid and name to appear at a minimum.

Reviewed by: freqlabs
Differential Revision: https://reviews.freebsd.org/D26756

flua: Add a libjail module

libjail is pretty small, so it makes for a good proof of concept demonstrating
how a system library can be wrapped to create a loadable Lua module for flua.

* Introduce 3lua section for man pages
* Add libjail module

Reviewed by: kevans, manpages
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D26080