Disable caching for individual actions

A pull request for issue #5.

When creating resource classes, users can specify a "cache" option for an action that will explicitly disable the cache behavior for that action:

```javascript
$cachedResource('issues', '/issues/:id', {id: '@id'}, {
    remove: { method: 'DELETE', cache: false }
});
```

By default, `cache` is assumed to be `true`.