Issue title: Beautify rendered html
 Issue body: Is there any interest/concern about the human-readability of the rendered HTML?
Not to undo the benefits gained from #202, but if we slightly relax the whitespace removal in Liquid templating, the indentation can be little bit easier on the eye.

For example, the blog posts on the home page currently render as:
```html
    <ul class="post-list"><li><span class="post-meta">May 20, 2016</span>
        <h3>
          <a class="post-link" href="/2016/05/20/welcome-to-jekyll.html">
            Welcome To Jekyll
          </a>
        </h3></li><li><span class="post-meta">May 20, 2016</span>
```
Removing a few select hyphens yields:
```html
    <ul class="post-list">
      <li>
        <span class="post-meta">May 20, 2016</span>
        <h3>
          <a class="post-link" href="/2016/05/20/welcome-to-jekyll.html">
            Welcome To Jekyll
          </a>
        </h3>
      </li>
```

A more extreme example is the social links in the footer:
```html
<div class="footer-col footer-col-2"><ul class="social-media-list"><li><a href="https://github.com/jekyll"><svg class="svg-icon grey"><use xlink:href="/assets/minima-social-icons.svg#github"></use></svg> <span class="username">jekyll</span></a></li><li><a href="https://twitter.com/jekyllrb"><svg class="svg-icon grey"><use xlink:href="/assets/minima-social-icons.svg#twitter"></use></svg> <span class="username">jekyllrb</span></a></li><li><a href="/feed.xml"><svg class="svg-icon grey"><use xlink:href="/assets/minima-social-icons.svg#rss"></use></svg> <span>rss</span></a></li></ul>
</div>
```
Altering the template a little (but not the rendered content) can result in:
```html
      <div class="footer-col footer-col-2"><ul class="social-media-list">
    <li><a href="https://github.com/jekyll"><svg class="svg-icon grey"><use xlink:href="/assets/minima-social-icons.svg#github"></use></svg> <span class="username">jekyll</span></a></li>
    <li><a href="https://twitter.com/jekyllrb"><svg class="svg-icon grey"><use xlink:href="/assets/minima-social-icons.svg#twitter"></use></svg> <span class="username">jekyllrb</span></a></li>
    <li><a href="/feed.xml"><svg class="svg-icon grey"><use xlink:href="/assets/minima-social-icons.svg#rss"></use></svg> <span>rss</span></a></li>
</ul>
</div>
```

Not perfect, but an improvement.

If you think it's worth the effort I can take a deeper look and submit a PR for review.
 Comments: 
 Comment 0: @KevinWMatthews I agree that Liquid's WhitespaceControl should be used with care in order to avoid losing HTML-source-readability points especially since GitHub Pages doesn't currently support any html-beautifier plugin.

A PR would be greatly appreciated.
 Comment 1: For those concerned with the HTML output, I'd recommend using https://github.com/apsislabs/jekyll-tidy (not supported by GitHub Page)
 Comment 2: > Shame it isn't supported by GitHub Pages.

Gladly, you can host your static Jekyll site for free elsewhere (Netlify is my favourite) withtout the current limitations of GitHub Pages.
 Comment 3: Cool, I recently started using Netlify for some content. It's been seamless so far.

I will confess, Minima is currently my favorite theme for GitHub Pages. I could set up a URL Netlify for each repo's docs, but for a small repo it is pretty convenient to just let GitHub do the work. Hmmm.
 Comment 4: 
This issue has been automatically marked as stale because it has not been commented on for at least two months.

The resources of the Jekyll team are limited, and so we are asking for your help.

If this is a **bug** and you can still reproduce this error on the <code>master</code> branch, please reply with all of the information you have about it in order to keep the issue open.

If this is a feature request, please consider whether it can be accomplished in another way. If it cannot, please elaborate on why it is core to this project and why you feel more than 80% of users would find this beneficial.

This issue will automatically be closed in two months if no further activity occurs. Thank you for all your contributions.

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