title: MongoKit: Unexpected behaviour when using use_schemaless together with use_dot_notation
body: <p>I am using MongoKit (v0.8.1) and am bit confused about the behaviour when defining a document with <code>use_schemaless=True</code> and <code>use_dot_notation=True</code>. MongoKit ignores any dynamic attributes (ie. anything that hasn't been defined in structure dict) when saving to the db. Works as expected when accessing the document via the usual square brackets. Obviously, I can work around this by overriding <code>__setattr__</code> but I find it a bit unexpected. Or is this intentional? Thanks!</p>