Adds an author to blog posts. (#209)

* Adds an author to blog posts.

See #113

* Feedback #209, fully contain author in {{with}}

Co-authored-by: Bud Parr <budparr@gmail.com>

layouts/_default/single.html

       <h1 class="f1 athelas mb1">
         {{- .Title -}}
       </h1>
+      {{ with .Params.author }}
+      <p class="tracked">
+         By <strong>{{ . | markdownify }}</strong>
+      </p>
+      {{ end }}
       {{/* Hugo uses Go's date formatting is set by example. Here are two formats */}}
       <time class="f6 mv4 dib tracked" datetime="{{ .Date.Format "2006-01-02T15:04:05Z07:00" }}">
         {{- .Date.Format "January 2, 2006" -}}