Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `README.md`:
  Upstream README has been changed, but we have a completely different one.
  Kept our `README.md`.
- `lib/sanitize_ext/sanitize_config.rb`:
  Upstream added support for more incoming HTML tags (a large subset of what
  glitch-soc accepts).
  Change the code style to match upstream's but otherwise do not change our
  code.
- `spec/lib/sanitize_config_spec.rb`:
  Upstream added support for more incoming HTML tags (a large subset of what
  glitch-soc accepts).
  Kept our version, since the tests are mostly glitch-soc's, except for cases
  which are purposefuly different.

lib/sanitize_ext/sanitize_config.rb

@@ -73,12 +73,11 @@ class Sanitize
       elements: %w(p br span a abbr del pre blockquote code b strong u sub sup i em h1 h2 h3 h4 h5 ul ol li),
 
       attributes: {
-        'a'          => %w(href rel class title),
-        'span'       => %w(class),
-        'abbr'       => %w(title),
+        'a' => %w(href rel class title),
+        'span' => %w(class),
         'blockquote' => %w(cite),
-        'ol'         => %w(start reversed),
-        'li'         => %w(value),
+        'ol' => %w(start reversed),
+        'li' => %w(value),
       },
 
       add_attributes: {