Added the Renderable mixin because DRY

src/documents/mixins.py

@@ -0,0 +1,9 @@
+class Renderable(object):
+    """
+    A handy mixin to make it easier/cleaner to print output based on a verbosity
+    value.
+    """
+
+    def _render(self, text, verbosity):
+        if self.verbosity >= verbosity:
+            print(text)