Throw events when a book and quill item is edited or signed.  Adds BUKKIT-1995

Fire events when MC|BEdit or MC|BSign custom packets are received.  Uses three new events in Bukkit: PlayerBookEvent (abstract), PlayerBookEditEvent and PlayerBookSign Event.

Implements: https://bukkit.atlassian.net/browse/BUKKIT-1995
Bukkit PR: https://github.com/Bukkit/Bukkit/pull/756
Test Plugin: https://github.com/desht/testbookevents