add details plugin

_plugins/cd.rb

@@ -42,7 +42,7 @@ EOF
           svg = File.read("#{dir}/optimized_cd.svg")
           return <<EOF
 <figure class="cdfig">
-  <img class="cd" style="width: #{@scale}%;" src="data:image/svg+xml;base64#{Base64.encode64(svg)}" alt="A commutative diagram"/>
+  <img class="cd" style="width: #{@scale}%;" src="data:image/svg+xml;base64,#{Base64.encode64(svg)}" alt="A commutative diagram"/>
   <figcaption>#{@caption}</figcaption>
 </figure>
 EOF

_plugins/details_tag.rb

@@ -0,0 +1,23 @@
+# from http://movb.de/jekyll-details-support.html
+module Jekyll
+  module Tags
+    class DetailsTag < Liquid::Block
+
+      def initialize(tag_name, markup, tokens)
+        super
+        @caption = markup
+      end
+
+      def render(context)
+        site = context.registers[:site]
+        converter = site.find_converter_instance(::Jekyll::Converters::Markdown)
+        caption = converter.convert(@caption).gsub(/<\/?p[^>]*>/, '').chomp
+        body = converter.convert(super(context))
+        "<details><summary>#{caption}</summary>#{body}</details>"
+      end
+
+    end
+  end
+end
+
+Liquid::Template.register_tag('details', Jekyll::Tags::DetailsTag)