Fix #91 by passing all rdflib types in six.text_type function

[xavierfigueroav]

1. About fixing:

• Pass all rdflib types in RDF parsers into six.text_type function before passing them into RDF builders.

2. About tests:

• Add test utilities that build a Python dictionary representation of the information stored in models.
• Add a JSON file with expected info after parsing a test file.
• Add tests that open a test file, open the expected file and compare them.

Signed-off-by: Xavier Figueroa xavierfigueroav@gmail.com

[xavierfigueroav]

A test is currently failing due to the change in the license list version format. Waiting until #103 is merged.

[pombredanne]

Thanks!