rework ifd handling and deprecate directly accessing ifds #46

	# Lifted from Documenter.jl docs
	# https://juliadocs.github.io/Documenter.jl/dev/man/hosting/#gh-pages-Branch
	# Apache licensed and located at
	# https://github.com/CliMA/TimeMachine.jl/blob/4d951f814b5b25cd2d13fd7a9f9878e75d0089d1/.github/workflows/DocCleanup.yml
	name: Doc Preview Cleanup

	on:
	pull_request:
	types: [closed]

	jobs:
	doc-preview-cleanup:
	runs-on: ubuntu-latest
	steps:
	- name: Checkout gh-pages branch
	uses: actions/checkout@v2
	with:
	ref: gh-pages

	- name: Delete preview and history
	run: \|
	git config user.name "Documenter.jl"
	git config user.email "documenter@juliadocs.github.io"
	git rm -rf "previews/PR$PRNUM"
	git commit -m "delete preview"
	git branch gh-pages-new $(echo "delete history" \| git commit-tree HEAD^{tree})
	env:
	PRNUM: ${{ github.event.number }}

	- name: Push changes
	run: \|
	git push --force origin gh-pages-new:gh-pages

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