Improve TS typings

[qqilihq]

These TS typing improvements address the following:

• Consider that usually a Promise is passed to the expressAsyncHandler function. Without this fix newer ESLint versions will produce the following error:

  Promise returned in function argument where a void return was expected  @typescript-eslint/no-misused-promises

• Pass Express’ generics for P, ResBody, ReqBody, and ReqQuery to the wrapped handler function. This provides an additional level of type-safety if being used:

  const handler = async (
   req: express.Request<{ foo: string; bar: number }>,
   res: express.Response
  ): Promise<void> => {
    // req.params.foo is string
    // req.params.bar is number
    // ...
  };
  
  router.get<{ foo: string; bar: number }>('/:foo/:bar', asyncHandler(handler));
  // gives error:
  router.get<{ foo: string; bar: string }>('/:foo/:bar', asyncHandler(handler));

[jhurliman]

Can this be merged?

[dko-slapdash]

@Abazhenov Could you please merge this one? Otherwise the library makes no sense in the latest Express v4.

[Abazhenov]

Thank You :)