Add gems and rocks

This is my first attempt at doing some fleshing-out of content as recommended. I tried to find if I needed to do anything to make the new categories (`treasure/gem` and `treasure/rock`) work but didn't come across anything. The levels are somewhat arbitrary but I tried to use my best RP judgment. I couldn't find `Color.CYAN` so I looked up the RGB value of cyan to see if I could add it myself. Google tells me it's rgb(0, 255, 255) which is already listed under Color.AQUA so I just went with that for Turquoise Stone. Also, I noticed Malachite Stone was commented as dark cyan but looked it up and I think it should be light green? (http://en.wikipedia.org/wiki/Malachite under Color on the right)