Biome Colors

Added biome colors to the renderer. The colors are read from a file named biome-colors.txt very similar to block-colors.txt
The file can also be specified via command line option.
A line in biome-colors.txt has an optional third parameter to control the biome color applied.
So if it's preferred to have no diffrent biome colors it's enough to either edit the block-colors.txt or set all biomes in biome-colors.txt to the same values.

I got the color values for the biomes from the respective vanilla image, but I had to adjust the swamp colors by just trying until I thought it looked right.

Here is a sample render with default settings:
![big](https://f.cloud.github.com/assets/3699551/376481/eccf7f04-a437-11e2-89a7-6801a754eeed.png)