MNT: Modernize

TST: Move CI to Actions

* MNT: Replace master with main

* Revert out-of-scope changes

Change css styling to render dropdown menu horizontal instead of vertical

Update layout.html file in sphinx to add top menubar to astropy docs

Remove deprecated use of script_files

Update sphinx URL that gets redirected

Replaced sphinx URL in footer by the "new" sphinx-doc.org domain

Fix button to hide output in documentation code blocks

CSS fixes for documentation overflows

Fix for issue #179

Fix css for Sphinx 1.3

Fix invalid HTML

Update favicon to multi-res for HiDPI displays

Better HiDPI support.

Use SVG for logo and linkout, falling back to PNG if the browser doesn't
support it.

Fix CSS formatting of "Other Parameters" section

"Other parameters" sections have weird formatting

Fix monospaced fonts in docs

Use the system monospace font in the docs

Adding "hide prompt and output" feature for docs codeblocks

Add warning on top of every file in astropy/sphinx

Initial implementation of astropy_helpers

Sphinx inline code css

On chrome, http connection will not work if the page is being viewed
with https (e.g. if you are...

Make docs logo text a theme configuration option

Changed front doc page to remove "Welcome" part of title

Change docs fixed width to a maximum width

Remove explicit inclusion of theme css file

"Edit page on github" reformat

Adjust docs so "[edit this page on github]" appears next to "Page Source"

Add a maximum width to the main text body in the docs

Fix issue 575

Updated logos to new versions

Move documentation theme to astropy.sphinx package
(so affiliated packages can use it)

static fixes

Updated docs theme to be consistent with astropy homepage