+0.3:
+ * Scrolls to the right so you can zoom ahead.
+ * Fully random rock generation; rocks no longer wrap vertically.
+ * Rocks' relative speeds are now uniform in all directions (i.e. much more
+ up/down speed variation). Noticeably hard...err...more "interesting".
+ * Command-line option --game-speed.
+
+0.4:
+ * Rocks now bounce off each other, and are pushed by particles.
+ * Now with two difficulties: normal and easy.
+ * Better new ship placement after you die.
+
+0.5:
+ * lots of bug fixes
+ * tweaks to engine and explosion graphics and new font