CLN/DOC: convert GH* issue mentions to the extlinks version
CLN/DOC: move release notes to docs
CLN: remove ability to refer to pull requests by sphinx roles
CLN/DOC: change links to release notes in CONTRIBUTING and whatnews
CLN: remove :hidden: and change release to markdown
Merge pull request #3961 from cpcloud/github-issue-sphinxext

DOC/CLN: remove gh links and use the new issue format for whatsnew
CLN: fix grammar in extract_index error message
TST: update test to reflect error message change
Merge pull request #3972 from cpcloud/fix-error-msg

CLN: fix grammar in extract_index error message
TST: Change network decorator to auto-check for network errors

TST: Enforce more strict rules about ignoring IOErrors with network tests
TST: Remove explicit connectivity checks in test cases.

Instead, network decorator in pandas.util.testing checks
for that instead. You have to opt into failing on tests
by setting `pandas.util.testing._FORCE_NETWORK_ERROR` to `True`.

CLN: Move imports and test skip to top of file
ENH: Allow keyword arguments to network decorator

ENH: skip try/except checks if raise_on_error
ENH: Add test decorator 'with_connectivity_check'.

Allows tests to check that a url is available before bubbling up
an error from a test case.
TST: Change tests to use with_connectivity_check to better approximate previous behavior
TST: Add check_before_test option to with_connectivity_check.
DOC: Update docs with changes