Make Adyen.httpclient module Python 3 compatible (#25)

* Make urlencode import Python 2/3 compatible

* Make urllib2 import Python 2/3 compatible

* Make StringIO import Python 2/3 compatible

* Add missing urlopen import

Author: woochica

Adyen/httpclient.py

@@ -12,10 +12,23 @@
 except ImportError:
     pycurl = None
 
-import urllib2
+try:
+    # Python 3
+    from urllib.parse import urlencode
+    from urllib.request import Request, urlopen
+    from urllib.error import HTTPError
+except ImportError:
+    # Python 2
+    from urllib import urlencode
+    from urllib2 import Request, urlopen, HTTPError
+
+try:
+    # Python 3
+    from io import StringIO
+except ImportError:
+    # Python 2
+    from StringIO import StringIO
 
-from urllib import urlencode
-from StringIO import StringIO
 import json as json_lib
 import re
 import base64
@@ -223,7 +236,7 @@ def _urllib_post(self, url,
         raw_store = json
 
         raw_request = json_lib.dumps(json) if json else urlencode(data)
-        url_request = urllib2.Request(url,data=raw_request)
+        url_request = Request(url,data=raw_request)
         if json:
             url_request.add_header('Content-Type','application/json')
         elif not data:
@@ -248,8 +261,8 @@ def _urllib_post(self, url,
 
         #URLlib raises all non 200 responses as en error.
         try:
-            response = urllib2.urlopen(url_request, timeout=timeout)
-        except urllib2.HTTPError as e:
+            response = urlopen(url_request, timeout=timeout)
+        except HTTPError as e:
             raw_response = e.read()
 
             return raw_response, raw_request, e.getcode(), e.headers