remove duplicate Firebase constructors (re-use references)
add missing urlError method
save the original Backbone.sync reference as sync_AJAX
updated documentation
add ability to unbind (dispose) a Collections event handlers and stop listeting to Firebase if they are no longer needed.
Corrected path processing for Backbone.sync CRUD ops, fixes #9
Merge pull request #8 from katowulf/master

remove duplicate Firebase constructors (re-use references)