Add "autoplay" option to embedded player

app/views/asciicasts/show.js.erb

@@ -29,6 +29,10 @@
     if (speed) {
       params += '&speed=' + speed;
     }
+    var autoplay = script.getAttribute('data-autoplay');
+    if (autoplay === '1') {
+      params += '&autoplay=' + autoplay;
+    }
 
     return params;
   }

app/views/docs/embedding.html.slim

@@ -52,3 +52,15 @@ markdown:
   For example, to make the font big the script should look like this:
 
       <script type="text/javascript" src="https://asciinema.org/a/14.js" id="asciicast-14" async data-size="big"></script>
+
+  ### autoplay
+
+  The `autoplay` option allows for automatic playback start when the player
+  loads. Accepted values:
+
+  * 0 - do not start playback automatically (default)
+  * 1 - start playback automatically
+
+  For example, to make the asciicast auto play:
+
+      <script type="text/javascript" src="https://asciinema.org/a/14.js" id="asciicast-14" async data-autoplay="1"></script>