Add a Makefile to generate classes doc in various formats

All the generated documentation is put in doc/_build.

doc/tools/makehtml.py

@@ -1,3 +1,6 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
 import sys
 import xml.etree.ElementTree as ET
 from xml.sax.saxutils import escape, unescape
@@ -29,7 +32,7 @@ for arg in sys.argv[1:]:
   input_list.append(arg)
 
 if len(input_list) < 1:
-  print("usage: makehtml.py <class_list.xml>")
+  print("usage: makehtml.py <classes.xml>")
   sys.exit(0)