Skosprovider-heritagedata

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- Fix an issue where calls that include a `language` parameter would fail because
certain methods were not expecting extra keyword parameters. (12)
- Some documentation clarifications. (11)

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- Compatibile with `SkosProvider 0.5.0 <http://skosprovider.readthedocs.org/en/0.5.0>`_.
- Each Concept or Collection now also provides information on the ConceptScheme
it's part of.
- Fix some issues with UTF-8 encoding.
- Fixed some issues with Python 2.x/3.x compatibility.
- Provider now throws a ProviderNotAvailableException when the underlying service is down.

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- Initial version
- Compatible with `SkosProvider 0.3.0 <http://skosprovider.readthedocs.org/en/0.3.0>`_.