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 it read from a file on disk instead? If you use `(testpath/"filename").write` that's the easiest way to write to a file. It's also failing because it's writing to `/tmp` and not cleaning up: http://bot.brew.sh/job/Homebrew%20Pull%20Requests/18100/version=yosemite/testReport/junit/brew-test-bot/yosemite/test_tippecanoe/