Feature request: extend from custom adapter

[sebamarynissen]

I have a use case we're I have a custom adapter that extends from the default socket.io in memory adapter that I would like to use in combination with socket.io-redis. It's possible to add this functionality with full backwards compatibility as follows:

import { Adapter } from 'socket.io-adapter';

export function extendFrom(BaseAdapter) {
  return class RedisAdapter extends BaseAdapter {
    // No other changes to the code required.
  };
}

export const RedisAdapter = extendFrom(Adapter);

I will try to file a PR for this, but I have no experience in TypeScript and my first attempts won't compile.

[darrachequesne]

I think we can now close this, as socketio/socket.io-adapter#66 was merged.