[CIVIS-5273] MAINT Windows builds on CircleCI

[jacksonlee-civis]

For CI, we used to have Windows builds through AppVeyor, but they haven't worked for a while (#279). Since CircleCI also provides Windows builds, let's just switch to CircleCI.

Resolves #279.

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• (For Civis employees only) Reference to a relevant ticket in the pull request title
• Changelog entry added to CHANGELOG.md at the repo's root level
• Description of change in the pull request description
• If applicable, unit tests have been added and/or updated
• The CircleCI builds have all passed

[Drew-Pappas]

Reviewed build-python-win on CircleCi and observed all tests passing. LGTM!