Reference implementation: InitialisePromise, fixes #109

Fixes #109:

> It seems that the [line after the catch()](https://github.com/domenic/promises-unwrapping/blob/7e434e4b/reference-implementation/lib/testable-implementation.js#L296) is supposed to call `resolvingFunctions["[[Reject]]"]` rather than `reject`.
> 
>  I also noticed that this specific part of the spec (draft) is not tested in the reference implementation's tests.