Add ServerListPingEvent player list API. Adds BUKKIT-5121, BUKKIT-2465
[Bleeding] Fix logic for calculating slot in Creative mode. Fixes BUKKIT-4715

Previously, hotbar slots for player inventory would return 9 - 18 while in
Creative mode, rather than 0 - 9. This commit fixes the logic used for
calculating the returned slot based on the raw slot.
Add methods to get and set knockback strength in Arrow. Adds BUKKIT-5103
Add setCritical and isCritical methods to Arrow.java. Adds BUKKIT-5113
[Bleeding] Add ProjectileSource interface. Addresses BUKKIT-1038, BUKKIT-1156
[Bleeding] Add setCharged and getCharged to WitherSkull. Adds BUKKIT-3060
Wither API. Adds BUKKIT-4571
Comment for getWitherHead() method
Event would be better as an extension of EntityTargetLivingEntityEvent
Slight alterations
Correct Javadoc Spacing
Enum docs
JavaDoc and formatting fixes per suggestions from @turt2live
Merge pull request #1 from lol768/entityWitherTarget

JavaDoc and formatting fixes per suggestions from @turt2live