TestFixture: Refactored temporary directory and file creation

Add TemporaryDirectoryCreator class, CreateTemporaryDirectory(), and
CreateFile().
Add data::Path

* Pull PathParts and related methods out of StringListOperations.
  There's now a public Path::Parts providing the functionality.
* Add some more public utility functionality to Path.
* Also add tests for Path.
StringTest: Small style fixes
Target: Add boundPath property and related methods
Add code::TargetBinder

It provides a utility method Bind(), which binds a target. Also add
tests.