Move geocode.py to tools/geocoding.py

Move geocoding capability into the tools module.
Remove unused imports.
Merge pull request #148 from jwass/geocoding_tools

Move geocode.py to tools/geocoding.py
Add explode() and collect() functions

explode() expands multi-part geometries into multiple rows, and into
their single part geometries.

collect() and take multiple single geometries and combine them into their
Multi* counterparts.
Add tests for collect()