This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
1. Import UART technical description from Frank Durda IV
<uhclem@nemesis.lonestar.org>.
2. Push existing sio chapter out of hw.sgml and make a separate
document out of it.
3. Make hw.sgml include the first two under serial devices section.
Submitted by: Frank Durda IV <uhclem@nemesis.lonestar.org> & I