Fix C extensions for Windows

Author: sdispater

pendulum/_extensions/_helpers.c

@@ -9,10 +9,6 @@
 #include <string.h>
 #include <time.h>
 
-#ifndef PyVarObject_HEAD_INIT
-    #define PyVarObject_HEAD_INIT(type, size) PyObject_HEAD_INIT(type) size,
-#endif
-
 /* ------------------------------------------------------------------------- */
 
 #define EPOCH_YEAR 1970
@@ -422,7 +418,7 @@ PyObject* timestamp(PyObject *self, PyObject *args) {
     result *= 60;
     result += second;
 
-    return PyLong_FromLong(result);
+    return PyLong_FromSsize_t(result);
 }
 
 PyObject* local_time(PyObject *self, PyObject *args) {

pendulum/helpers.py

@@ -1,14 +1,19 @@
 from __future__ import absolute_import
 
 import pendulum
+import os
 
 from math import copysign
 from datetime import datetime, date, timedelta
 from contextlib import contextmanager
 from typing import Union
 
+with_extensions = os.getenv("PENDULUM_EXTENSIONS", "1") == "1"
 
 try:
+    if not with_extensions:
+        raise ImportError()
+
     from ._extensions._helpers import (
         local_time,
         precise_diff,