Simplify Store#unregister stopListening

By only providing he one argument you can stopListening from any events all at once.
Remove overrides for Model.unset and Model.clear, since these use Model.set nowadays.
Delete `keySource` after a `set` as well. Fixes #322
Merge pull request #383 from philfreo/patch-4

Simplify Store#unregister stopListening
Fix `pop` on an empty collection. Ref #380
Create a change log in preparation for 0.8.6
Add PT_Sans webfont
Relations can now be a property or a method
Merge pull request #370 from gmajoulet/master

Relations can now be a method or a property
tests for dotNotation support for collections
dotNotation support for collection indexes
Add option to define `relatedModel` or `collectionType` as a function
Backbone-relational 0.8.6
Merge in 0.8.6
Set version to 0.8.6a