Fixed iterable methods (all* + allNullOr*) types (return and $value parameter).

[jmfeurprier]

This should make all $value parameters back to mixed (like in v1) for methods all* and allNullOr*, and iterable return types coherent for methods allNullOr*.

[shadowhand]

This looks good, but I need to think about it a bit. Technically, this would be a BC break in signature, which would require a version 3.0. But if we're going to do a new major, then I would rather be removing the inner static::isIterable($value) check instead.

[jmfeurprier]

Please see #337 (comment)

[shadowhand]

Released in version 2.1.2.