Merge pull request #250 from zhuowei/master

Fixed a few missing methods due to the Multiworld conversion fixed #248
Fixed #251 implode() error
Fixed #249
Fixed already loaded worlds
Index fix
Fixed getting spawn seed
Allow OPping disconnected players
Added MC_REMOVE_PLAYER
Fixed PMFLevel::getBlock() not converting to int
Fixed #254
New Level Generator API & Support for MC Superflat Presets
Updated pthreads version
Added trees to teh SuperflatGenerator
Fixed PMF metadata set
Fixed build
Added Perlin noise generator
Fixed #256 Signs not attaching to walls
Player spawning on unknown worlds will be redirected properly to the main world
Level Generation API updated
Plugin API: Allow Plugins without Main class