WIP on a common data representation for tiles
Finished implementation of new data representation for tiles;

- Renamed jsonExtractor to geoJson;
- Removed use of JSON everywhere except geoJson and MapzenVectorTileJson;
- Used glm::vec3 as basis of common coordinate data;
- Updated documentation of tileData.h;
- Modified geometry construction pipeline to produce geometry with coordinates normalized to the size of the enclosing tile (see tileData.h)
Some clean up for dataSource
Add warnings and a quick fix to disallow index overflows in buffers with more than 65535 vertices
Forward declaration in support of clean header
Removing MAGIC number

Removed 65535 and using sizeof(GLushort) to represent why we are doing this.
more magic number removal
Merge pull request #22 from tangrams/datareptile

Common Data Representation for Tiles