Work in progress on marking features to be merged back into their pre-tiling form

[e-n-f]

For mapbox/vector-tile-spec#104

To build:

git checkout reconstruct
make clean
make -j

There is a new --join-features-across-tiles flag to turn on the new features, but there is nothing to see yet: everything so far is just internal plumbing within Tippecanoe to track feature clipping, and there is nothing yet that even tries to reassemble the features that have been clipped apart.

[e-n-f]

Most of my work so far has been focused on polygons but I got stuck because they are the most complicated case.

New strategy: Get reconstruction working for LineStrings, and then generalize to other geometry types from there. Treat complete reconstruction of features as the main goal, and leave the other cases that can be done without complete reconstruction to be considered as potential optimizations, not goals of their own.