libxdg-basedir 1.2.0 (new formula)

Formula for the libxdg-basedir library which is an implementation of the XDG Base Directory specifications.
Can this test be modified to do something more substantial than e.g. `--version` or `--help`? See `cmake.rb` for an example of an application formula with a good test and `tinyxml2.rb` for an example of a library formula with a good test. Thanks!