Verify that byte and Unicode strings are used consistently.
Document how they are used.

The ``FileUri`` class is ugly.
Implement a nicer interface.

Add an example for using streams.

Improve the test suite.

   Track test coverage.

   Cython ≥ 0.23 provides the plugin ``Cython.Coverage``
   that can be added to ``.coveragerc``.

Improve the documentation.

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