add video shortcode

layouts/shortcodes/video.html

@@ -0,0 +1,20 @@
+<video 
+    class="video-shortcode" 
+    preload="{{ .Get "preload" | default "auto" }}" 
+    controls
+>
+    <source 
+        src="{{ .Get "src" }}" 
+        type="{{ .Get "type" }}"
+        {{ if or (.Get "alt") (.Get "caption") }}
+            alt="{{ with .Get "alt" }}{{ . }}{{ else }}{{ .Get "caption" | markdownify | plainify }}{{ end }}"
+        {{ end }}
+    >
+    {{ i18n "videoIsNotSupported" }}
+</video>
+{{ if .Get "caption" }}
+    <figcaption>
+        {{ .Get "caption" | markdownify }}
+    </figcaption>
+{{ end }}
+