docs/templates/layout.html: Indicate latest vs release docs.

When looking at latest (the default for docs.micropython.org), make it
clear that this isn't the release version.
 - Changes the version in the top-left to "latest".
 - Adds a message to the top of each page to explain.

For future release versions, add a short message to link to the latest
version.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

docs/conf.py

@@ -33,6 +33,7 @@ html_context = {
     'downloads':[
         ('PDF', url_pattern % micropy_version + '/micropython-docs.pdf'),
     ],
+    'is_release': micropy_version != 'latest',
 }
 
 
@@ -74,7 +75,7 @@ copyright = '- The MicroPython Documentation is Copyright © 2014-2022, Damien P
 #
 # We don't follow "The short X.Y version" vs "The full version, including alpha/beta/rc tags"
 # breakdown, so use the same version identifier for both to avoid confusion.
-version = release = '1.19.1'
+version = release = micropy_version
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.

docs/templates/layout.html

@@ -4,3 +4,28 @@
 {# we change the master_doc variable so that links to the index
    page are to index.html instead of <port>_index.html #}
 {% set master_doc = "index" %}
+
+{% block document %}
+  {% if is_release %}
+    <div class="wy-alert wy-alert-danger">
+      <p>
+        This is the v{{ release }} version of the MicroPython
+        documentation. The <a href="/en/latest/{{ pagename }}.html">latest
+        development version</a> of this page may be more current.
+      </p>
+    </div>
+  {% else %}
+    <div class="wy-alert wy-alert-danger">
+      <p>
+        This is the documentation for the latest development branch of
+        MicroPython and may refer to features that are not available in released
+        versions.
+      </p>
+      <p>
+        If you are looking for the documentation for a specific release, use
+        the drop-down menu on the left and select the desired version.
+      </p>
+    </div>
+  {% endif %}
+  {{ super() }}
+{% endblock %}

docs/templates/topindex.html

@@ -5,8 +5,7 @@
   <h1>MicroPython documentation</h1>
 
   <p>
-    {{ _('Welcome! This is the documentation for MicroPython') }}
+    {{ _('Welcome! This is the documentation for MicroPython') }}{% if last_updated %}, {{ _('last updated') }} {{ last_updated|e }}{% endif %}.
-    v{{ release|e }}{% if last_updated %}, {{ _('last updated') }} {{ last_updated|e }}{% endif %}.
   </p>
 
   <p>