Fix documentation for memoized subject instances
Fix documentation for memoized subject instances

* This is not a class handling *all* memoizations.
  Just on especific cases where the memoization semantics had been
  set-up via the memoizable gem.

backus/mutest,backus/mutest,tjchambers/mutant,backus/mutant,nepalez/mutant,kbrock/mutant