preserve vertices that are forming horizontal or vertical segments
update 'next vertex horizontal/vertical test' and avoid bloating tiles
add test for multiple-subpaths encoding/decoding
add compatibility with mapnik 2.3.x
clean up comments
remove auto usage to maintain non-c++11 compile without warnings
Merge pull request #40 from mapbox/sharp_turns

Keep right angles oriented in cardinal directions no matter how high tolerance is set