Rewrote the basic section of the chapter on defining new types.

Rewrote the basic section of the chapter on defining new types.
Changed the example to show how to create types the new way:

- Use a class new method rather than a new function.

- Use self->ob_type->tp_free in deallocators

- Use attribute descriptors rather than set/getattr methods.

- Make the type usable as a base type.

I split the example into 3 parts:

1. The minimal new type

2. Adding attributes and methods.

3. Finer control over attributes.

It's much simpler to define builtin types. These updates hopefully
show this.

I also made minor wording changes in two other places.

I still need to update xxobject.c