Feature Request: Proportionally darken view as drawer slides

[thorst]

Using the amazon kindle app you can see the background view darken in real time as the drawer slides out and lighten in real time as the drawer slides in.

With REFrostedViewController the darkening and lightening is performed in a single animation.

To test this, simply tap & hold, and drag the menu the entire way out. Upon releasing you will see the background view darken quickly.

Would there be a way to make this act closer to the amazon kindle app?