as_integers and as_doubles should understand logical inputs

[vspinu]

Arguably logicals are also "integer like", but the main use case is the all-NA input vectors. When a user enters xyz(arg = NA) and arg is intended to be an integer the cpp level conversion with as_integers fails.

For this reason as_integers is still incomplete because we still need a custom wrapper around as_integer for logicals internally.

Would be really great if it could be done as part of #265 (cc @DavisVaughan)