#84 Add Futures support for partial completion (sort registry)

[Neil Avery]

This might be needed when requesting from an unknown
set of peers (x) and a result count of 10 is all that
is required.

i.e.
get(10 /* results */, 1000 /* wait for 1 sec */)

[Neil Avery]

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implemented but need to add support for a non-annotated version.