title: Flask MongoKit 'Collection' object is not callable
body: <p>I am following this <a href="http://pythonhosted.org/Flask-MongoKit/" rel="nofollow">http://pythonhosted.org/Flask-MongoKit/</a> as an example </p>
  
  <p>I am just trying to get an instance of Document for writing unit test, but it isn't working. Here's the code for test:</p>
  
  <pre><code>import unittest
  from tests import app, db, ctx
  from word.models import Word
  
  class ModelWordTestCase(unittest.TestCase):
  
      def setUp(self):
          pass
  
      def test_model_word(self):
          print db.Word
  
          word = db.Word()
  
          self.assertIsNotNone(word)
  
      def tearDown(self):
          pass
  </code></pre>
  
  <p><strong>Word Class</strong></p>
  
  <pre><code>from flask.ext.mongokit import Document
  from core import db
  
  @db.register
  class Word(Document):
      __collection__ = 'words'
      use_dot_notation = True
  
      STATUS = {
          "approved" : 1,
          "pending" : 0,
          "rejected" : -1,
      }
  
      structure = {
          'lang': unicode,
          'local': unicode,
          'pronunciation' : unicode,
          'meaning': unicode,
          }
  </code></pre>
  
  <p>Surprisingly db.Word exists when printed with <code>print db.Word</code> statement, but it can't be called to create a new instance as done in tutorial I mentioned above. Here's the output of test:</p>
  
  <pre><code>Collection(Database(MongoClient('localhost', 27017), u'words_test'), u'Word')
  
  E
  ======================================================================
  ERROR: test_model_word (tests.model_tests.ModelWordTestCase)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "tests/model_tests.py", line 14, in test_model_word
      word = db.Word()
    File "/usr/local/lib/python2.7/dist-packages/mongokit/collection.py", line 64, in __call__
      self.__name)
  TypeError: 'Collection' object is not callable. If you meant to call the 'Word' method on a 'Database' object it is failing because no such method exists.
  
  ----------------------------------------------------------------------
  Ran 1 test in 0.002s
  
  FAILED (errors=1)
  </code></pre>
  
  <p>How can I fix this and get instance of Word document so that I can create and save a record.</p>