Apparently fmt.Sscanln doesn't parse bool's properly and this isn't
likely to be fixed by the Go team who regard sscanf as a mistake.
This only uses sscan for integers and uses the correct routine for
everything else.
This also implements parsing time.Duration
See: https://github.com/golang/go/issues/43306
This is possible now that we no longer support go1.12 and brings
rclone into line with standard practices in the Go world.
This also removes errors.New and errors.Errorf from lib/errors and
prefers the stdlib errors package over lib/errors.
