Fixed #184 Django 1.11 LTS

I know that Django 1.11 has D-FF built in. However I and many other
require a tranistion build of D-FF. This commit does this

floppyforms/widgets.py

@@ -45,6 +45,23 @@ class Widget(forms.Widget):
     def is_hidden(self):
         return self.input_type == 'hidden' if hasattr(self, 'input_type') else False
 
+    def render(self, name, value, attrs=None):
+        """
+        Returns this Widget rendered as HTML, as a Unicode string.
+        The 'value' given is not guaranteed to be valid input, so subclass
+        implementations should program defensively.
+        """
+        raise NotImplementedError('subclasses of Widget must provide a render() method')
+
+    def build_attrs(self, extra_attrs=None, **kwargs):
+        """
+        Backported from Django 1.10
+        Helper function for building an attribute dictionary.
+        """
+        attrs = dict(self.attrs, **kwargs)
+        if extra_attrs:
+            attrs.update(extra_attrs)
+        return attrs
 
 class Input(Widget):
     template_name = 'floppyforms/input.html'