feat: display author avatar images in blog post (#204)

* feat: support displaying author images in blog post

* chore: fix typo

* chore: run build:css

* refactor: support both plain author list

* chore: run build:css

* chore: add support for local avatar images

* chore: update css classes

exampleSite/content/blog/markdown.md

@@ -2,8 +2,12 @@
 title: Markdown Syntax Guide
 date: 2020-01-01
 authors:
-  - name: John Doe
-    link: https://example.com/johndoe
+  - name: imfing
+    link: https://github.com/imfing
+    image: https://github.com/imfing.png
+  - name: Octocat
+    link: https://github.com/octocat
+    image: https://github.com/octocat.png
 tags:
   - Markdown
   - Example