Additional bindings go in "cytoolz/cpython.pxd".

I would actually like to use different names for the C API functions defined in that file.  For example, perhaps function names should use `PyPointer_` prefix if the new binding returns a pointer, such as:
```python
cdef extern from "Python.h":
    PyObject* PyPointer_GetItem "PyObject_GetItem" (object o, object key)
```
Is this common practice, and what naming conventions make sense?