Document PyObject_New(), PyObject_NewVar(), PyObject_Init(),

Document PyObject_New(), PyObject_NewVar(), PyObject_Init(),
PyObject_InitVar(), PyObject_Del(), PyObject_NEW(),
PyObject_NEW_VAR(), and PyObject_DEL().

Add notes to PyMem_Malloc() and PyMem_New() about the memory buffers
not being initialized.

This fixes SF bug #439012.

Added explicit return value information for PyList_SetItem(),
PyDict_SetItem(), and PyDict_SetItemString().  Corrected return type
for PyList_SET_ITEM().

Fixed index entries in the descriptions of PyLong_AsLong() and
PyLong_AsUnignedLong().

This fixes the API manual portion of SF bug #440037.

Note that the headers properly declare everything as 'extern "C"' for
C++ users.

Document _Py_NoneStruct.

Added links to the Extending & Embedding manual for PyArg_ParseTuple()
and PyArg_ParseTupleAndKeywords().

Added note that PyArg_Parse() should not be used in new code.

Fix up a few style nits -- avoid "e.g." and "i.e." -- these make
translation more difficult, as well as reading the English more
difficult for non-native speakers.