clarify that Memoizers always take ownership of a callable#7

Closed

bkietz wants to merge 2 commits intopitrou:ARROW-10655-lru-cachefrom

bkietz:ARROW-10655-lru-cache

Commits on Feb 9, 2021

ARROW-10655: [C++] Add cache and memoization facility
pitrou
committed

Commits on Feb 17, 2021

clarify that Memoizers always take ownership of a callable
bkietz
committed