add inner prop

allows inner shortcodes to be used

layouts/shortcodes/code.html

@@ -8,7 +8,11 @@
       {{ if .Get "title" }}<span class="collapsable-code__title">{{ .Get "title" | markdownify }}</span>{{ end }}
       <span class="collapsable-code__toggle" data-label-expand="{{ .Get "expand" | default "△" }}" data-label-collapse="{{ .Get "collapse" | default "▽" }}"></span>
     </label>
+    {{ if .Get "inner" }}
+    {{ .Inner }}
+    {{ else }}
     <pre {{ if .Get "language" }}class="language-{{ .Get "language" }}" {{ end }}><code>{{ .Inner | string }}</code></pre>
+    {{ end }}
   </div>
 {{ else }}
   {{ errorf "If you want to use the \"collapsable code\" shortcode, you need to pass a mandatory \"language\" param. The issue occured in %q (%q)" .Page.File .Page.Permalink }}