Since times now accepts a required and a maximum number of calls, it can
replace at_{least,most}, reducing its API surface, which is internal
anyway.

... since times just delegated to update

This reverts commit 9d0d37a. 'times'
expresses the responsibility of this method better, but had to be
renamed earlier due to the introduction of a public method with the same
name. That method is now gone, so we can revert to the original name.

By translating all other cardinality methods to the times method, we
clarify both that all the other methods are merely syntactic sugar, and
that they all set the lower and upper limits to the number of calls.

Closes freerange#476