Condensed changes:
* Translation updates
* Various code cleanup
* Fix movement using the diagonal keys on keypads
* Initialise the horizontal key movement speed properly
* Documentation improvements
* Add support for playing on a keyboard to the SDL backend.
* Add a new fourth level
* Various minor bugfixes
* Change the high scores file from a memory dump to plain text.
Users with an existing high scores file in memory dump format will
have their high scores file converted to plain text on startup.
You are captain of the cargo ship Chromium B.S.U., responsible for
delivering supplies to our troops on the front line. Your ship has a
small fleet of robotic fighters which you control from the relative
safety of the Chromium vessel.
(Incredibly slow even on a fast machine -- turn off details and make
the window small if you want to play it.)
