Tidied up ThermometerSpec ScaldingSupport and added some documentation.
Adds `withArgs` to ScaldingSupport.

Added a function to help create scalding job with the default and custom args.
Changes `withArgs` in ScaldingSupport to be type paramterised.
Fixes wrong test failure message for PathFacts.

Previously, most of the messages in PathFact would say the path exists
even though there were no files.