Fix `vectorize_where` bug and RTD config #58

Job	Run time
precommit / Load tox environments	5s
test / Load tox environments	6s
precommit / pre-commit (ubuntu-latest)	37s
test / py38 (macos-latest)	4m 0s
test / py310 (macos-latest)	3m 26s
test / py38 (windows-latest)	3m 54s
test / py310 (windows-latest)	4m 10s
test / py38 (ubuntu-latest)	2m 0s
test / py39 (ubuntu-latest)	2m 15s
test / py310 (ubuntu-latest)	2m 12s
docs / Load tox environments	6s
test_full_database / Load tox environments	4s
test_full_database / py310 (ubuntu-latest)	6m 22s
docs / build_docs (ubuntu-latest)	2m 18s
publish	0s
	31m 35s

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