Merge two commits in

0c4e5c38cbaa83e4b8602f2eb7bfb3049d3e52e5 - Change
WorldConfig.biomeConfigs from HashMap to simple array for better
performance

0c4e5c38cbaa83e4b8602f2eb7bfb3049d3e52e5 - Added new setting to biome
config - RiverBiome.