Remove monkey-patch and add custom pandoc renderer

renderers/markdown.moon

@@ -0,0 +1,23 @@
+class PandocRenderer extends require "sitegen.renderers.markdown"
+  unescape_cosmo = @unescape_cosmo
+  escape_cosmo = @escape_cosmo
+
+  command: "pandoc"
+
+  render: (page, md_source) =>
+    md_source = page\pipe "renderer.markdown.pre_render", md_source
+    md_source, escapes = escape_cosmo md_source
+
+    markup_filename = os.tmpname!
+    input_handle = io.popen @command .. " > " .. markup_filename, "w"
+    input_handle\write md_source
+    input_handle\close!
+
+    output_handle = io.open markup_filename, "r"
+    result = output_handle\read "*a"
+    output_handle\close!
+
+    html_source = assert result
+    html_source = unescape_cosmo html_source, escapes
+
+    super page, html_source