Add highlighting of GFM code blocks with mistune

IPython/nbconvert/filters/markdown.py

@@ -90,8 +90,22 b' def markdown2html(source):'
     else:
         return markdown2html_pandoc(source)
 
+if mistune is not None:
+    from pygments import highlight
+    from pygments.lexers import get_lexer_by_name
+    from pygments.formatters import HtmlFormatter
+
+    class MyRenderer(mistune.Renderer):
+        def block_code(self, code, lang):
+            if not lang:
+                return '\n<pre><code>%s</code></pre>\n' % \
+                    mistune.escape(code)
+            lexer = get_lexer_by_name(lang, stripall=True)
+            formatter = HtmlFormatter()
+            return highlight(code, lexer, formatter)
+
 def markdown2html_mistune(source):
-    return mistune.markdown(source)
+    return mistune.Markdown(renderer=MyRenderer()).render(source)
 
 def markdown2html_pandoc(source):
     """Convert a markdown string to HTML via pandoc"""