Update to Future 0.12. Now chaining methods must be called in non-void context. Fix t/30-chained.t.
Strict: explicitly mark subfutures as "failure handled" in wait_all, wait_any, needs_all, needs_any methods. It can be problematic to treat failed subfutures as "not handled", because handling failed subfutures would involve no "on_fail" or "on_ready" callbacks. Instead, their failures would be inspected directly, which is difficult to detect. Therefore, treating all subfutures as "handled" is more consistent and immune to changes in the original Future.
t/50-repeat.t: now Future::Utils::repeat must accompany "return" option.
t/10-construction.t: now Future::Utils::repeat must accompany "return" option.