[docs] [issue15029] Update Defining New Types chapter according to PEP 253

Mateusz Loskot added the comment: Similar request has been rejected in response to the Issue 621526 [1], but I'm not proposing to include PEP into docs, but to update and improve docs with material discussed in accepted PEPs. [1] http://bugs.python.org/issue621526 ---------- _______________________________________ Python tracker http://bugs.python.org/issue15029 _______________________________________