Dawg

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- fix installation under PyPy (note: DAWG is slow under PyPy
and may have bugs).

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- small tweaks for docstrings;
- the extension is rebuilt using Cython 0.18.

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- small improvements to ``.compile_replaces`` method;
- benchmarks for ``.similar_items`` method;
- the extension is rebuilt with Cython pre-0.18; this made
``.prefixes`` and ``.iterprefixes`` methods faster
(up to 6x in some cases).

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- tests are included in source distribution;
- benchmark results in README was nonrepresentative because of my
broken (slow) Python 3.2 install;
- installation is fixed under Python 3.x with ``LC_ALL=C`` (thanks
Jakub Wilk).

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Internal tweaks: memory usage is reduced; something is a bit faster,
something is a bit slower.

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Storage scheme is updated to match DAWG==0.5. This enables
the alphabetical ordering of ``BytesDAWG`` and ``RecordDAWG`` items.

In order to read ``BytesDAWG`` or ``RecordDAWG`` created with
versions of DAWG < 0.5 use ``payload_separator`` constructor argument::

>>> BytesDAWG(payload_separator=b'\xff').load('old.dawg')