Support Python 2.5 and Python 3
* Update init module function.
* Use `PyObject_Hash` function to get hash instead of access `ob_shash` directly.
* Use `PyLong_FromLong` instead of `PyInt_FromLong`. (PyInt_FromLong is removed since Python 3)
* `PySlice_GetIndicesEx` accept `PyObject*` as first argument instead of `PySliceObject*`.
* Use `Py_TYPE` macro instead of access `ob_type` directly. (Add `Py_TYPE` definition for Python 2.5)
* Use `PyVarObject_HEAD_INIT(&PyType_Type, 0)` instead of `PyObject_HEAD_INIT(&PyType_Type)`. (Add `PyVarObject_HEAD_INIT` definition for Python 2.5)
* Update `PySequenceMethods` mapping. (`sq_slice` and `sq_ass_slice` are removed since Python 3)
* Update `PyNumberMethods` mapping. (Some functions are removed since Python 3)