Add compat.py and fix Python 3 error

{{cookiecutter.app_name}}/requirements/prod.txt

@@ -20,7 +20,6 @@ WTForms==2.0
 
 # Deployment
 gunicorn>=17.5
-wsgiref>=0.1.2
 
 # Assets
 Flask-Assets==0.10

{{cookiecutter.app_name}}/{{cookiecutter.app_name}}/compat.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+"""Python 2/3 compatibility module."""
+
+
+import sys
+
+PY2 = int(sys.version[0]) == 2
+
+if PY2:
+    text_type = unicode
+    binary_type = str
+    string_types = (str, unicode)
+    unicode = unicode
+    basestring = basestring
+else:
+    text_type = str
+    binary_type = bytes
+    string_types = (str,)
+    unicode = str
+    basestring = (str, bytes)

{{cookiecutter.app_name}}/{{cookiecutter.app_name}}/database.py

@@ -5,6 +5,7 @@ utilities.
 from sqlalchemy.orm import relationship
 
 from .extensions import db
+from .compat import basestring
 
 # Alias common SQLAlchemy names
 Column = db.Column