Version 0.31 Released

This is a tiny update to fix a potentially game-breaking bug and tweak a few things:

• I forgot to make the BioFuel globules dropped by barrels persistent objects!! This is a pretty big oversight. If you broke a barrel and then left the room without collecting the globules they'd be gone forever, resulting in a softlock. Now they'll still be there if you leave the room and come back.
• I also forgot to make the barrels drop fewer, larger globules, because it was too easy to miss one or two of the tiny ones they dropped a whole bunch of! Now they drop 4 big globules, in a smaller radius, with a slightly larger pickup distance.
• I made Key Items require you to hold the Use key to pick up, instead of an auto-pickup, so you can see what they are before collecting them. Before it was too easy to pick up a key item without noticing.
• A couple tiny adjustments to the height/weight display code, to hopefully play nice with commas being used as a decimal separator. Still.