[docs] include structmember.h in Python.h (issue 2897)

[storchaka+cpython at gmail.com]

http://bugs.python.org/review/2897/diff/18779/Doc/extending/newtypes.rst
File Doc/extending/newtypes.rst (right):

http://bugs.python.org/review/2897/diff/18779/Doc/extending/newtypes.rst#newcode1155
Doc/extending/newtypes.rst:1155: (defined in the :file:`structmember.h`
header), the attribute is read-only; otherwise
Too long line.

http://bugs.python.org/review/2897/diff/18779/Doc/extending/newtypes.rst#newcode1156
Doc/extending/newtypes.rst:1156: it should be set to `0`.
``0``

http://bugs.python.org/review/2897/