Added PlayerBookEvent, PlayerBookEditEvent & PlayerBookSignEvent.
Events related to book & quill and written book items.
https://bukkit.atlassian.net/browse/BUKKIT-1995

Changes as requested by evilmidget38

oldBookMeta -> previousBookMeta

Collapsed new book edit events into single PlayerEditBookEvent
As per discussion with Wolvereness and evilmidget38

Added throws declarations to setNewBookMeta() and associated Javadoc

More updates as requested by gmcferrin/Wolvereness