syslinux changes

* /etc/MBR/syslinux -> /etc/syslinux
  everybody and their dog expects it there,
  i'm not getting into this uphill battle
* syslinux.cfg uses absolute paths
  same thing works from both /etc/{MBR,}/syslinux/syslinux.cfg
example config with less gay slice names
$software list expanded a bit
example: $destdir left commented out

hardcoded "/mnt" is prone to conflicts with other uses
main sequence short-circuits on failure
refresh pacman's keys, $software update

i3-wm install bombed because the package was signed with
an unknown key or what, so that's solved.  plus some other
new packages.
embeds syslinux.cfg template

the template is mostly static, with menu entries copied from
the archlinux-created config, and custom theming (text mode only).
--syslinux <configfile> prints syslinux.cfg on stdout

configfile is necessary (syslinux.cfg embeds some values).
needs to call locale-gen(1) in the installed system

i had that in my PoC implementations, dropped it accidentally
somewhere along the way.