Fix documentation for withFileAsOutput

So I see you changed the signature of `withFileAsOutput` again. Documentation was a bit screwy, minor patch attached.

While we're at it, I thought I might mention that the "Ext" suffix seems a bit abrupt. Rather than `withFileAsOutputExt` I might suggest `withFileAsOutputFull`... that is, if you don't want to use a `'` character, as in `withFileAsOutput'`

AfC