RDoc will automatically format and link API references as long as they
are not already marked up as inline code.
This commit removes markup from various API references so that those
references will link to the relevant API docs.
* Improve ActionText::FixtureSet documentation
Support for Action Text attachments in fixtures was added by [76b33aa][] and
released as part of [6.1.1][], but has not yet been documented.
This commit documents the `ActionText::FixtureSet` for the API
documentation, and mentions it in the Rails Guides pages.
[76b33aa]: 76b33aa3d1
[6.1.1]: https://github.com/rails/rails/releases/tag/v6.1.1
* Fix indention of comments
Co-authored-by: David Heinemeier Hansson <david@loudthinking.com>