Added *_entity_spec(), *_projectile_owner(), *_projectile_does_bounce(), get_mob_target()

Added *_entity_spec(), *_projectile_owner(), *_projectile_does_bounce(), get_mob_target().
Added player_toggle_flight, player_toggle_sneak, player_toggle_sprint, player_velocity and plugin_disable events.
Refactored abstraction of entities.
Minor changes: moved psetop() from Meta to PlayerManagement, player_pre_login now uses AsyncPlayerPreLoginEvent instead of PlayerPreLoginEvent (deprecated), set_pvelocity() throws a RangeException if the magnitude of the velocity passed in is greather than 10.