Improve dbotu module docs

[cduvallet]

The documentation for interfacing with dbotu3 via the python module is relatively sparse.

For example, the dbotu module has no docstring (from an ipython terminal):

>>> import dbotu
>>> dbotu?
Type:        module
String form: <module 'dbotu' from '/Users/claire/anaconda/bin/dbotu.pyc'>
File:        ~/anaconda/bin/dbotu.py
Docstring:   <no docstring>

The API Reference documentation could also be greatly improved with use cases and/or examples.