Version 0.5b

New features:

• There is now rain and fog.
• The sailing model has been tuned to address the issue raised here. In particular, fore-and-aft sails produce less thrust.
• Also the ship is a little lighter, and square-sails can be a touch closer to the wind before they start shaking.
• Dates and distances of noon observations are shown on the map.
• Cities are marked in the world.
• Guns start off housed.

Also various tweaks and bugfixes; time should now pass properly; guns are slower to reload.