Handbook conversion

[Justin C. Sherrill]

I've pulled over the FreeBSD Handbook and made sure it will build within our
doc framework.  I've made some cosmetic stabs at it, but a lot of it is
still FreeBSD-specific - everything after about half-way through the
introduction, in fact.

http://www.forknibbler.com/handbook/

I'd like to commit this, since it would be very easy for other folks to jump
in and convert any small section.  Hope springs eternal...  I'll commit
this tomorrow, if nobody says otherwise.