- Add tests for FoldResult
- Make documentation more explicit
- Assert failure accumulator in test
Submitted-by: Matthew Piziak <matthew.piziak@gmail.com>
Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
This introduces the `FoldResut` trait to move from `func(receiver, ...)`
style to `receiver.func(...)` style. Also add a means to pass the
default result explicitly.
