Refactor and new Features -
  - Built with 1.5.1-R0.2
  - Implemented ability to limit by mob group
    -- (ANIMAL, WATER_MOB, MONSTER, AMBIENT)
  - Implemented "removeOldest" config.
    -- On by Default
    -- If off, new spawn is blocked.
  - Implemented more effective means of counting mobs in chunks.
    -- Each relevant chunk only checked once now.
    -- If "removeOldest" is off, then count is stopped as soon as limit
       is detected.