5.0.0
* New itertools:
* :func:split_into
* :func:unzip
* :func:substrings
* Changes to existing itertools:
* :func:ilen was optimized a bit
* :func:first_true now returns None by default. This is the reason for the major version bump - see below.
* Other changes:
* Some code for old Python versions was removed
* Some documentation mistakes were corrected
* Tests now run properly on 32-bit versions of Python
* Newer versions of CPython and PyPy are now tested against
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