Unstable update and stuff

In this update...

• Gold ore blocks now produce gold ore, which must be smelted.

• Gold blocks join copper and iron blocks.

• New biome - wetlands. Occurs where land is relatively low and wet.

• New plant - bamboo. Grows in wetlands.

• Employee info screen is now tabbed and includes some additional info.

• Backpack isn't a separate dialog, and shows icons.

• Digging now requires dwarves to equip picks. Miners come with a pick already so you won't notice - but this is the first step toward equipable items.

• Why not make tables and chairs out of peppermint??

• Kill things on the debug menu now uses the selection buffer so it will be more useful if you've got a pest problem.

• Sliders on options screen show a value (where it makes sense)

• Added confusing slider for species limit - 100% means 100% of the default limit of 15.

• Building floor will now queue up a dig task first.

• Fixed bug that let creatures spawn without beyond species limit.

• Fixed bug that made craft icons vanish.

• Added hotkey (esc) that closes popups.