* Problem: Source files contain no license info
Solution: Add comments with SPDX license info to source files
* Python 3 files don't need # -*- coding: utf-8 -*-
* Problem: No docs explaining use of MongoDB for querying
Solution: Start a new root docs page explaining how a node operator can use the full power of MongoDB's query engine, and can expose as much of that as they like to end users.
* Finished first draft of new docs page 'Querying BigchainDB'
