apply function to elements in parallel using futures

 Implementations of apply(), by(), eapply(), lapply(), Map(), mapply(),
 replicate(), sapply(), tapply(), and vapply() that can be resolved using
 any future-supported backend, e.g. parallel on the local machine or
 distributed on a compute cluster. These future_*apply() functions come
 with the same pros and cons as the corresponding base-R *apply()
 functions but with the additional feature of being able to be processed
 via the future framework.