Memoize the bisect test functions

[mikebentley15]

It is challenging to memoize the algorithm generically since it depends on what is in the elements list. Instead, we should have the function that is passed in memoize its input-output pairs (which is the same as saying we should cache previously computed results). This allows the bisect algorithm to not have to keep old results around, but can rather call the test function again. It simplifies the generic algorithm at the expense of creating the test function it uses. This will help when we go to implement delta debugging as well (see #171).

[mikebentley15]

Addressed by pull request #190