Add support for XDG_CONFIG_HOME in _platform module. Ref #99. This functionality won't be enabled until the 4.0 release

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extra : amend_source : 75bfe83d2ab43dff8f8eb80a3a829cc03548860d
Update docs to reflect actual location of config and data files. Ref #99.

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extra : amend_source : 6ada8b77feef28bde9db84632c1df5c04f5f0190
Added tag 3.5 for changeset 05cb255d5395
Bumped to 3.6 in preparation for next release.