message: Optimize loading docs.rs-specific javascript
  This removes the [type] attribute, which is not recommended by MDN since JavaScript is the default anyway, and loads it [async] instead of blocking.
  [type]:
  [async]:
diff: -<script type="text/javascript" src="/-/static/menu.js?{{ docsrs_version() | slugify }}"></script>
  -<script type="text/javascript" src="/-/static/index.js?{{ docsrs_version() | slugify }}"></script>
  +<script async src="/-/static/menu.js?{{ docsrs_version() | slugify }}"></script>
  +<script async src="/-/static/index.js?{{ docsrs_version() | slugify }}"></script>
  {# see comment in ../storage-change-detection.html for details #}
  <iframe loading="lazy" src="/-/storage-change-detection.html" width="0" height="0" style="display: none"></iframe>
  