helmet

Is there any reason why we can't move the typespec from https://github.com/DefinitelyTyped/DefinitelyTyped to this repo so we do not have to deal with two packages.

We could copy that into this package and add "types": "./lib/main.d.ts" in the package.json

I've been researching into this for a day or two now, and believe the type for FilledContext needs to have the helmet property as optional like so:

export type FilledContext = {
  helmet?: HelmetData;
};

I believe this because if you follow the instructions in the Usage section of the README, we create an empty `helmetCon