Big patch:
 - replace Python types by C Python types (eg. str => PyUnicodeObject* and None => Py_None)
 - fix "w" / "w*" / "w#" doc: similar to "y" / "y*" / "y#" (and not "s" / "s*" / "s#")
 - add quotes to the formats, eg. s => "s"
 - use :ctype: to add links to some terms (eg. Py_BEGIN_ALLOW_THREADS) and use a fixed width font
 - replace "the default encoding" by "'utf-8' encoding"
 - replace true by 1, and false by 0 (C API of Python doesn't use stdbool.h but classic int)
 - use a list for the two modes of "es#"
 - Py_BuildValue(), "s" and "s#" formats: specify that the Python object is a str

1 and 0 were formatted with ``1`` and ``0``. I don't understand why, so I removed the italic style.

Sorry for the length of the patch, but it was easy to work on only one aspect.