Added entity_line_of_sight(), entity_can_see(), *_entity_air(), *_entity_max_air(), generate_tree(), *_gamerule(), *_PVP(), *_difficulty() and shutdown_server().
Fixed NPE in all_entities(), spawn_mob() and drop_item() (due to inexisting world or invalid sender).
Added the possibility to choose a world for all_players().
Added the possibility to keep the random seed in create_word() if we want to choose the environment or the generator, and to set a string for seed (will be its hashcode).
Added the possibility to choose the way the item will be spawned in drop_item().
Fixed gamemode lists in documentation.
ploc() now returns an associative array, like all other location arrays.
Moved *_difficulty, *_PVP and *_gamerule functions from Minecraft to World class, and removed shutdown_server.
Re-added and optimized server_shutdown(), and fixed a test that was failing due to the ploc() modification.
Updated doc, forgot a line
Merge pull request #162 from Hekta/master

Added entity_line_of_sight(), entity_can_see(), *_entity_air(), *_entity...