Use alt text when formatting headers with an rdoc-image.

Author: ioquatix

lib/rdoc/markup/heading.rb

@@ -66,7 +66,13 @@ def label context = nil
   # element.
 
   def plain_html
-    self.class.to_html.to_html(text.dup)
+    text = self.text.dup
+
+    if text.match?(/rdoc-image:[^:]+:(.*)/)
+      text = text.match(/rdoc-image:[^:]+:(.*)/)[1]
+    end
+
+    self.class.to_html.to_html(text)
   end
 
   def pretty_print q # :nodoc: