New formula: tippecanoe, a tool for map data processing

This adds a new formula for Eric Fischer's tippecanoe project.
The project depends on protocol buffers and sqlite, takes
GeoJSON as input and produces MBTiles as output.
Can you write to a file (using `Pathname.write`) and read from that instead? Also, you can write to just `blank.mbtiles` in the same directory as it'll be cleaned up after the test is run.