Adding a new Rate Limiter Store 
Hi

I'm trying to extend this library with a new store for Dynamodb. I'm trying to do this from my application. However, when I extend class RateLimiterStoreAbstract I can't access `this.points` due to the following error: `Property 'points' does not exist on type`.

Do you know how I can do it?

Regards
Esteban