Drop Python 2

[jrbourbeau]

Closes #219

TODO:

• Unit tests and/or doctests in docstrings
• tox -e py38 passes locally
• tox -e py27 passes locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• tox -e docs passes locally
• AppVeyor and Travis CI passes
• Test coverage to 100% (Coveralls passes)

[jakirkham]

FWIW I'm ok skipping the macOS bit and saving that for another PR. Maybe mark it as a known failure though?

[jrbourbeau]

Sounds good! I've skipped the OSX build in this PR and have switched to using GitHub Actions over in #221

[alimanfoo]

Looks good, so cathartic!

One small thought, there is still a Buffer class in numcodecs/compat_ext.pyx. That class was originally created to work around some buffer support differences between PY2 and PY3, although we must've removed some of that compatibility code a while back as no longer needed after we did some work upstream in the ensure_contiguous_array() function. In any case, it's probably worth keeping the Buffer class because it provides some convenience. However, the docstring for the class is a bit out of date now, probably worth fixing to clarify that it's just a convenience class, nothing to do with compatibility.

[jrbourbeau]

Thanks for reviewing @alimanfoo! I've updated the docstring for Buffer to indicate it's just a convenience class and also removed some lingering Python 2 references in documentation and our tox setup

[jakirkham]

Thanks James for the PR and Alistair for the review! 😄

[joshmoore]

Looks like readthedocs is going to need updating to use python 3 as well: https://readthedocs.org/projects/numcodecs/builds/11416597/

Edit: fixed in https://readthedocs.org/projects/numcodecs/builds/11743058/ by changing the interpreter.

[jakirkham]

Thanks Josh 😄