GitBook development seems a bit stuck right now so let's switch to VuePress which, IMO, is more user friendly. Update the documentation to include the version number in which features were added and use custom container to display notes and warnings.
Call the given `functor` on each element in the promise value (i.e. `Sequence<T>`), then resolve to the original sequence unmodified. Also provide a static helper to directly filter values (`QtPromise::each(values, functor)`).
