Removed unused ReferenceManager
Implemented creeper abilities

* Creepers now explode with a sound effect
* Creepers drop a music disc on the unlikely event of being killed by a
skeleton's arrow

Inspired by @maniak89's PR #132.
Fixed mobs too close to player not ticking

A condition would never be fulfilled. A number squared was compared to
-1, but there is nothing that, multiplied by itself, gives -1.
Large reworking of mob code [SEE DESC]

+ Implemented better pathfinding
- Removed lots of unused variables, functions, etc.
* Changed some variable types
* Other miscellaneous fixes, and also completes the previous PRs
Monsters no longer check for direct line of sight
Made wolves compatible with new AI code
Changed a condition to IsGameMode
Miscellaneous improvements
Zombies and skeletons use AI
Fixed a generator bug
All mobs now drown (fixes #54)

* Implemented mob drowning
* Iron Golems and squids are excluded
Mob bugfixes

* Mobs no longer require constant line-of-sight to a player to remain
aggravated
* Fixed an ASSERT
* Fixed mobs jumping
* Fixed Idle state not properly using AI
+ Added FILE_IO_PREFIX to favicon loading
+ Implemented #563
Implemented pickup combining

* Fixes FS393
* Part of  #131
Attack() is no longer always called
Implemented fall damage for mobs

+ Implemented mobile fall damage
* Formatting fixes
+ Defined new Position->Integer macros
Two minor changes
Did what xoft recommended
Merge pull request #587 from mc-server/mobimprovements

Mob improvements & rudimentary artificial intelligence