Moved over existing tests to use `sinon-chai`
Merge pull request #27 from matthojo/tests

Moved over existing tests to use `sinon-chai`
- Data is now loaded dynamically from the OSM Overpass API
- Buildings have a height value taken from OSM tags
- Geo library has been refined
- Objects are rendered in correct positions (not at 0,0 with child objects offset)
- Other tweaks and improvements related to Overpass addition
Updated readme
Tidied up files after Overpass update
- Added rivers to Overpass request
- Added fallback Overpass API endpoint
- Features change colour depending on type
- Refined worker batching process
Added more natural features and fixed height issues
First pass at a tile-based loading mechanism
Added todos
Adding debug flag
Added zoom control (closes #16)
- Added panning using mouse controls
- Moved Geo projection center so Three.js coodinates start at 0,0 (was causing accuracy errors with panning)

Closes #13
Tidying up
Updating readme
Added notes for panning rendering fixes
Updated zoom logic
Implemented orbit controls (closes #14 & #15)
Added Slack to Travis
First pass at a grid-loading mechanism
First pass at cache and feature duplication detection