feat: add embed video support

Author: cotes2020

_includes/embed/twitch.html

@@ -0,0 +1,4 @@
+<iframe class="embed-video twitch lazyload"
+  src="https://player.twitch.tv/?video={{ include.id }}&parent={{ site.url | split: '://' | last | remove: '/' }}"
+  frameborder="0" allowfullscreen="true"
+  scrolling="no"></iframe>

_includes/embed/youtube.html

@@ -0,0 +1,6 @@
+<iframe class="embed-video youtube lazyload"
+  src="https://www.youtube.com/embed/{{ include.id }}"
+  title="YouTube video player"
+  frameborder="0"
+  allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
+  allowfullscreen></iframe>

_sass/addon/commons.scss

@@ -576,6 +576,21 @@ i { /* fontawesome icons */
   }
 }
 
+.embed-video {
+  width: 100%;
+  height: 100%;
+  border-radius: 4px;
+  margin-bottom: 1rem;
+
+  &.youtube {
+    aspect-ratio: 16 / 9;
+  }
+
+  &.twitch {
+    aspect-ratio: 310 / 189;
+  }
+}
+
 /* --- buttons --- */
 .btn-lang {
   border: 1px solid !important;