Consider interop between `retry.__` suite and possible `retryable(fn, params)` signature

[parzhitsky]

Interesting: currently, the retry() function accepts an action parameter, which is a function with promise-constructor-executor-like signature:

// roughly
type Action = <Result>(resolve: Function, reject: Function, retry: Retrier) => Promise<Result>;

// roughly
type Executor = <Result>(resolve: Function, reject: Function) => Promise<Result>;

This means, that it would be backward compatible to provide those params as the second argument of retry(), as in:

const result = await retryable(db.connect, { retryDelay: ... });

… which frankly should've been the first choice of the function signature.

Originally posted by @parzhitsky in #96 (comment)