Introduce Temporary.using for ensuring directory cleanup after use

Raised from Ivory [PR comment](https://github.com/ambiata/ivory/commit/79699cfcf8c80b77000865c8108036425249684c#commitcomment-6873287)

/cc @markhibberd @maxpow4h 
AfterExample doesn't really work nicely with scalacheck properties, it was being worked around with `isolated`. I like yours better. You might have to check, but you can probably remove the `isolated` tag as well.