erltrek_ship: link with commander.

If either ship or commander process dies, the other should die too,
so using a link makes more sense than monitors.
refactor shell commands.

The shell commands now provide their own result processing functions.

Fix bug in that short/long range scans where not returned as result
to the ship command, but sent as a sync event on the side.

This did not play out well for the klingons,
that look at the data programmatically..
fix broken help command.