Clarify version docs (#955)

This PR updates the home page and the CHANGELOG to refer to  v0.4.0.rc1 as a pre-release or release candidate, rather than a release. See [this comment](https://github.com/just-the-docs/just-the-docs/pull/613#issuecomment-1240442518) for motivation.

It also adds the versioned docs issue (#728) to the roadmap in the CHANGELOG.

As the config for the theme docs now needs to declare callouts, the [callouts docs](https://just-the-docs.github.io/just-the-docs/docs/ui-components/callouts/) can now illustrate the rendered appearance. (These callouts are merely examples: the names and colors should eventually be replaced by a principled collection, taking account of WCAG.)

docs/ui-components/callouts.md

@@ -9,7 +9,10 @@ nav_order: 7
 
 Markdown does not include support for callouts. However, you can style text as a callout using a Markdown extension supported by kramdown: [*block IALs*](https://kramdown.gettalong.org/quickref.html#block-attributes). 
 
-Common kinds of callouts include `admonition`, `attention`, `caution`, `danger`, `error`, `hint`, `important`, `note`, `tip`, and `warning`.
+Common kinds of callouts include `highlight`, `important`, `new`, `note`, and `warning`.
+
+{: .warning }
+These callout names are *not* pre-defined by the theme: you need to define your own names.
 
 When you have [configured]({{ site.baseurl }}{% link docs/configuration.md %}#callouts) the  `color` and (optional) `title` for a callout, you can apply it to a paragraph, or to a block quote with several paragraphs, as illustrated below.[^postfix]
 
@@ -24,6 +27,10 @@ When you have [configured]({{ site.baseurl }}{% link docs/configuration.md %}#ca
 A paragraph
 ```
 
+{: .highlight }
+A paragraph
+
+
 #### A single paragraph callout
 {: .no_toc }
 
@@ -32,6 +39,9 @@ A paragraph
 A paragraph
 ```
 
+{: .note }
+A paragraph
+
 ```markdown
 {: .note-title }
 > My note title
@@ -39,6 +49,11 @@ A paragraph
 > A paragraph with a custom title callout
 ```
 
+{: .note-title }
+> My note title
+>
+> A paragraph with a custom title callout
+
 #### A multi-paragraph callout
 {: .no_toc }
 
@@ -51,6 +66,13 @@ A paragraph
 > The last paragraph
 ```
 
+{: .important }
+> A paragraph
+>
+> Another paragraph
+>
+> The last paragraph
+
 ```markdown
 {: .important-title }
 > My important title
@@ -62,19 +84,31 @@ A paragraph
 > The last paragraph
 ```
 
+{: .important-title }
+> My important title
+>
+> A paragraph
+>
+> Another paragraph
+>
+> The last paragraph
+
 #### An indented callout
 {: .no_toc }
 
 ```markdown
-> {: .hint }
+> {: .highlight }
   A paragraph
 ```
 
+> {: .highlight }
+  A paragraph
+
 #### Indented multi-paragraph callouts
 {: .no_toc }
 
 ```markdown
-> {: .attention }
+> {: .new }
 > > A paragraph
 > >
 > > Another paragraph
@@ -82,6 +116,14 @@ A paragraph
 > > The last paragraph
 ```
 
+> {: .new }
+> > A paragraph
+> >
+> > Another paragraph
+> >
+> > The last paragraph
+
+
 #### Nested callouts
 {: .no_toc }
 
@@ -91,6 +133,10 @@ A paragraph
 > A paragraph
 ```
 
+{: .important }
+> {: .warning }
+> A paragraph
+
 #### Opaque background
 {: .no_toc }
 
@@ -102,3 +148,10 @@ A paragraph
 > A paragraph
 > </div>
 ```
+
+{: .important }
+> {: .opaque }
+> <div markdown="block">
+> {: .warning }
+> A paragraph
+> </div>