fix typos and other cosmetic issues (#214)

cosmetic issues:
- reST headlines' underline length needs to match the headline length
  (looks like somebody is / was using a proportional font)
- Cython code lines do not need to be terminated with a semicolon
- always use triple-double-quotes for docstrings

test/test_extension.py

@@ -42,7 +42,7 @@ def test_extension_type():
             typecode = 123 # application specific typecode
             data = obj.tostring()
             return ExtType(typecode, data)
-        raise TypeError("Unknwon type object %r" % (obj,))
+        raise TypeError("Unknown type object %r" % (obj,))
 
     def ext_hook(code, data):
         print('ext_hook called', code, data)