{{ background }} format AND avatar path

brower rendered the background css style in HTML file

BEFORE:
<pre><code class="language-html">
<style type="text/css">body {background-image:url(
      /images/
    
      bg.jpg
    
  
    );}</style>
<code></pre>


AFTER:
<pre><code class="language-html">
<style type="text/css">body {background-image:url(/images/bg.jpg);}</style>
</code></pre>

I'm not quite sure that I want to do this. I like having the ability to let people choose their image from a local or an external source.

We could, though, do something like what's being done in the `background_image.html` file where it checks for `'//'` and then decides on whether it's a local or an external link.

In fact, this comes up so often that I was thinking about making a separate include for it, and going back through and plugging it into the places that could benefit from it.