Defines an intbitset data object to hold unordered sets of unsigned
integers with ultra fast set operations, implemented via bit vectors
and Python C extension to optimize speed and memory usage.

Emulates the Python built-in set class interface with some additional
specific methods such as its own fast dump and load marshalling
functions.  Uses real bits to optimize memory usage, so may have
issues with endianness if you transport serialized bitsets between
various machine architectures.

Please note that no bigger than __maxelem__ elements can be added to
an intbitset and, if CFG_INTBITSET_ENABLE_SANITY_CHECKS is disabled,
you will receive unpredictable results.

>>> x = intbitset([1,2,3])
>>> y = intbitset([3,4,5])
>>> print x & y
intbitset([3])
>>> print x | &
intbitset([1, 2, 3, 4, 5])
