Fix some documentation bugs.

- It's FileInfo.{to,from}WindowsSeparator*s* (plural), of course.
- It is plain wrong that the "inputs" and "outputs" variables are
mutually exclusive with "input" and "output", respectively, and it would
not make sense either.

Change-Id: I00c6eca9a6207cb50d5258834e4dfdc7a4345c8e
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>