Bitarray

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* add Python 2.4 support
* add (module level) function bitdiff for calculating the difference
between two bitarrays

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* add iterdecode method (C level), which returns an iterator but is
otherwise like the decode method
* improve memory efficiency and speed of pickling large bitarray objects

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* add buffer protocol to bitarray objects (Python 2.7 only)
* allow slice assignment to 0 or 1, e.g. `a[::3] = 0` (in addition to
booleans)
* moved implementation of itersearch method to C level (Lluis Pamies)
* search, itersearch now only except bitarray objects,
whereas `__contains__` excepts either booleans or bitarrays
* use a priority queue for Huffman tree example (thanks to Ushma Bhatt)
* improve documentation

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* fixed MSVC compile error on Python 3 (thanks to Chris Gohlke)
* add missing start and stop optional parameters to index() method
* add examples/compress.py

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* update documentation to use tobytes and frombytes, rather than tostring
and fromstring (which are now deprecated)
* simplified how tests are run

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* added itersearch method
* added Bloom filter example
* minor fixes in docstrings, added more tests