Bitarray

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* add `bitarray.util.serialize()` and `bitarray.util.deserialize()`
* allow whitespace (ignore space and `\n\r\t\v`) in input strings,
e.g. `bitarray('01 11')` or `a += '10 00'`
* add `bitarray.util.pprint()`
* When initializing a bitarray from another with different bit-endianness,
e.g. `a = bitarray('110', 'little')` and `b = bitarray(a, 'big')`,
the buffer used to be simply copied, with consequence that `a == b` would
result in `False`. This is fixed now, that is `a == b` will always
evaluate to `True`.
* add test for loading existing pickle file (created using bitarray 1.5.0)
* add example showing how to [jsonize bitarrays](../examples/extend_json.py)
* add tests

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* fix issue 114, raise TypeError when incorrect index is used during
assignment, e.g. `a[1.5] = 1`
* raise TypeError (not IndexError) when assigning slice to incorrect type,
e.g. `a[1:4] = 1.2`
* improve some docstrings and tests

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* add `bitarray.util.urandom()`
* raise TypeError when trying to extend bitarrays from bytes on Python 3,
i.e. `bitarray(b'011')` and `.extend(b'110')`. (Deprecated since 1.4.1)

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* add missing .h files to sdist tarball, 113

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* use `Py_SET_TYPE()` and `Py_SET_SIZE()` for Python 3.10, 109
* add official Python 3.10 support
* fix slice assignment to same object,
e.g. `a[2::] = a` or `a[::-1] = a`, 112
* add bitarray.h, 110

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* use PyType_Ready for all types: bitarray, bitarrayiterator,
decodeiterator, decodetree, searchiterator