Improve 'promise' mode with thenInjection option

[medikoo]

/cc @Kovensky

If used implementation doesn't implement done and finally then it's not possible to do both:

• Return promise as returned by original function
• Register callbacks for internal use without muting eventual Unhandled error events.

The workaround could be, to provide a special mode for promise handling, in which user will agree that memoized function will return extended promise from original and not exactly one returned by original function.

[Rush]

I just suffered from memoizee using the .done and me using Bluebird. Bluebird will do process.exit inside .done. http://bluebirdjs.com/docs/api/done.html "any unhandled rejection that ends up here will crash the process (in node)"

With bluebird one can use http://bluebirdjs.com/docs/api/reflect.html in order to find the resolved value without side effects.

Above was a reply to #59 (comment)

[medikoo]

@Rush Just setup memoization with promise: 'then' option, and it'll be fine.
It's documented: https://github.com/medikoo/memoizee#promise-returning-functions

[medikoo]

@Rush I've improved internal handling, so now by default when using Bluebird then:finally mode will be used. done mode is not recommended (and since v0.4.7 not applied by default) for reasons you mentioned (unconditional crashing in case of rejections)

[Rush]

@medikoo thank you! exciting