split iterators-and-generators into 2 chapters, added stubs for introduction to python classes (in iterators chapter)

--HG--
rename : iterators-and-generators.html => generators.html

index.html

@@ -27,9 +27,9 @@ h1:before{content:""}
 <li><a href=native-datatypes.html>Native Datatypes</a>
 <li><a href=strings.html>Strings</a>
 <li><a href=regular-expressions.html>Regular Expressions</a>
-<li><a href=iterators-and-generators.html>Iterators <i class=baa>&amp;</i> Generators</a>
+<li><a href=generators.html>Generators</a>
+<li><a href=iterators.html>Iterators</a>
 <li><a href=advanced-iterators.html>Advanced Iterators</a>
-<li class=todo>Objects and object-orientation
 <li><a href=unit-testing.html>Unit Testing</a>
 <li class=todo>Test-first programming
 <li><a href=refactoring.html>Refactoring</a>