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
Register plugin — key/val store for Models/Collections and monkey patching of relation methods to support string inputs
Fix for #204 and #197, helpful Errors thrown for invalid Models
Rename plugin: register => registry
Merge pull request #199 from valet-io/feature/model-registry

Allows models to be registered with a string name
Fixes #206
Merge pull request #205 from tgriesser/errors

Fix for #204 and #197, helpful Errors thrown for invalid Models
Adding link to the virtuals documentation
Merge pull request #209 from johanneslumpe/documentation-changes

Added virtuals to the docs and linked to the wiki
Code cleanup/rewording of plugins.
Allow external plugins with Bookshelf.plugin
Remove unused AMD build script
Groups related by pivot's id on belongsTo through relation.

When the relation is `belongsTo through` on eager loading,
groups related models by pibot's id.
This would make it possible to fetch the related model's data
by eager loading on `belongsTo through` relation and
fixes issue #214.
Updated relation type docs
Merge pull request #216 from johanneslumpe/documentation-changes

Updated relation type docs
Merge pull request #215 from p-baleine/topic-belongsTo-through

Groups related by pivot's id on belongsTo through relation.
update copyright year
Merge pull request #219 from gdi2290/patch-1

Copyright: 2013 => 2014