Add deprecated and new-feature "badges"

[sethkinast]

Some sort of small HTML (web component? probably not) that we can apply to documentation.

<new-feature version="2.6.2" /> Dust allows Promises to be passed as part of your context. When a Promise is found...
<div class="badge new-feature">2.6.2</div> Dust allows Promises to be passed as part of your context. When a Promise is found...