Scrapinghub

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- remove official support for Python 2.7, 3.5, 3.6 and 3.7
- add official support for Python 3.11 and 3.12
- use the ``SHUB_APIURL`` and ``SHUB_STORAGE`` environment variables as default
values when available
- fix the warning when ``msgpack`` is not installed (used to say
``msgpack-python``)

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- add Python 3.10 support
- improve ``iter()`` fallback in getting the ``meta`` argument

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- update msgpack dependency
- drop official support for Python 3.4
- improve documentation, address a few PEP8 complaints

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- add `items.list_iter` method to iterate by chunks
- fix retrying logic for HTTP errors
- improve documentation

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- use `jobs.cancel` command name to maintain consistency
- provide basic documentation for the new feature

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- add a command to cancel multiple jobs per call
- normalize and simplify using VCR.py cassettes in tests