This adds support for a `<d-topics-list>` tag you can embed in your site
that will be rendered as a list of discourse topics. Any attributes on
the tag will be passed as filters. For example:
`<d-topics-list discourse-url="URL" category="1234">` will filter to category 1234.
To use this feature, enable the `embed topics list` site setting. Then
on the site you want to embed, include the following javascript:
`<script
src="http://URL/javascripts/embed-topics.js"></script>`
Where `URL` is your discourse forum's URL.
Then include the `<d-topics-list discourse-url="URL">` tag in your HTML document and it will
be replaced with the list of topics.
