Makes 'db' argument to connection optional.
Merge pull request #737 from wcdolphin/master

Make 'db' argument to connection optional
Update changelog.rst
First pass at making BaseDict and BaseList work like their native counterparts

Python's `dict()` takes one arg and optional kwargs; similarly with `list()`.
The existing `BaseDict()` and `BaseList()` constructors break that signature.
This is first pass at getting it working for the simple case of passing in a
single arg.