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.