Updated docs on model.destroy

Updated docs to reflect that Model.destroy() takes an optional `options` object the same way Model.fetch() and Model.save() do
Calls to 'destroying' event handlers follow the same 3 variable pattern as others
Merge documentation changes
Merge branch 'master' of github.com:valet-io/bookshelf into valet-io-master

* 'master' of github.com:valet-io/bookshelf:
  Calls to 'destroying' event handlers follow the same 3 variable pattern as others
  Updated docs on model.destroy
Updating event catelog docs for destroying signature