Added dictionary-style access to documents

Added __init__.py info to package, moved TopLevelDocumentMetaclass
to base.py, added tests for dictionary-style access.

mongomap/__init__.py

@@ -0,0 +1,8 @@
+from document import Document
+import fields
+from fields import *
+
+__all__ = fields.__all__  + ['Document']
+
+__author__ = 'Harry Marr'
+__version__ = '0.1'