- rename all Linux bits to Posix, to make it clear, that is (should) work on
  any Posix system
- sprinkle a bit of BSD into device names and examples
- added define for a non-standard badurate 460800

Signed-off-by: Jasper Lievisse Adriaanse <jasper@humppa.nl>
Signed-off-by: Petr Stetiar <ynezz@true.cz>