Support the provision of multi-element paths in TemporaryFolder

We're currently working with a system that organises data files in a very hierarchical fashion. When writing tests for this system we were creating lots of verbose code to create test versions of these structures using `TemporaryFolder`. This encouraged us to modify this class so that it supports the provision of multi-element paths via a varargs parameter on the `newFile` and `newFolder` methods. This has greatly reduced the ugly boiler-plate on our side.

This change is backwards compatible with earlier versions of **lastcommons-test**.