Closes #82

##### 2.3.0 - 09 January 2014
- Caches can now be disabled #82
- The `options` object (`$angularCacheFactory()`, `AngularCache#setOptions()`, and `$angularCacheFactoryProvider.setCacheDefaults()`) now accepts a `disabled` field, which can be set to `true` and defaults to `false`.
- `$angularCacheFactory.enableAll()` will enable any disabled caches.
- `$angularCacheFactory.disableAll()` will disable all caches.
- A disabled cache will operate as normal, except `AngularCache#get()` and `AngularCache#put()` will both immediately return `undefined` instead of performing their normal functions.