integrate feedback

we can't fix then, but we can replace it.

instead of using immediately invoked anonymous asynchronous arrow functions, we can replace the then method with then-like helper functions. In fact, we can optimize these small helpers to the exact cases we need.

= after() => helper with only onFulfilled callback
= catchAfter => helper with onError callback that handles promise rejection
= tryAfter => helper with synchronous onFulfilled callback and onError callback that handles promise rejection and onFulfilled exceptions

Author: yaacovCR