Allow dynamic images on each blog post (#143)

* Allow dynamic images on each blog post

* Adding responsive CSS for blog post images

* Adding image parameter to YAML front matter

_config.yml

@@ -182,6 +182,13 @@ prose:
           help: "Enter date of post."
           placeholder: "yyyy-mm-dd"
           alterable: true
+      - name: "image"
+        field:
+          element: "text"
+          label: "Image"
+          help: "Add a thumbnail image to your post."
+          placeholder: "Thumbnail"
+          alterable: true
       - name: "published"
         field:
           element: "checkbox"