Fix a couple of jsHint warnings
Don't let a `null` on `key` override a value from `keySource`. Fixes #442
Add `getIdsToFetch` to RelationalModel. Ref #463
update years
Merge pull request #465 from RusAlex/530_update_years

update copyright years
Remove the dot notation syntax for getters; it just doesn't belong in the scope of BBR.
API change: make `fetchRelated` return a single promise. Ref #467
Add `fetchRelated` change to change log
Rename `key` to `attr` in some places, to correspond with Backbone's distinction.
Implement `getAsync` as a separate function on RelationalModel
Simplify `getAsync`; using Deferred.then with its `doneFilter` works great here.
Minor test rewrites so we can more easily test lazy loading with the Zoo/Animal models
Replace `fetchRelated` by `getAsync`. Update tests and docs as well. Ref #467
getAsync call options.error once

In error callback of getAsync call options.once. If there where no models created, just refreshed options.error was never called.
Merge pull request #473 from sventschui/master

getAsync call options.error once
Fix expected outcome on number of error callbacks triggered by getAsync
Update old comment referring to `relations` as a function. Ref #475
getAsync: avoid building 'stub' models whenever possible (because the collection can create a url when given a set of ids).
#setup needs to be called on subclasses of models as well.
Make sure model hierarchy is determined when needed and actually nullify reverse relations when model is destroyed.