title: Include "All other functions" in a pkgdown reference yaml
body: <p>I have a <code>pkgdown</code> site in which I group a number of functions into categories in the reference <code>.yml</code> file. I'm wondering if there is a way to put all of the functions which I didn't explicitly categorize into their own category. The only thought I had was to use the <code>matches</code> function like so:</p>
  
  <pre><code>reference:
  - title: "someCategory"
    contents:
    - myFunction
  - title: "other"
    contents:
    - matches(".*")
  </code></pre>
  
  <p>But this puts <code>myFunction</code> in both the "someCategory" and "other" categories. What I'd like to do is match all functions which aren't in a category. </p>
  
  <p>Thanks! </p>