Support Pathname and implicit File.join when passing filenames

[acant]

Any of the SugarUtils methods which accept filenames should accept the following:

• String
• Pathname
• array of Strings which will be File.join'ed
• multi-String parameters, which will be File.join'ed (where possible)

This should simplify the calls to SugarUtils methods.
Also consider implementing this functionality as a SugarUtils.ensure_pathname methods which can also be used outside the gem.