Fix overuse of file descriptors during recursive sorting

• Don't trust the OS so much about how many files can be open
• Fix -ar option not to accidentally cause recursive sorting

Add attribution option, and more work on low-memory performance

• Limit the size of the parallel parsing streaming input buffer
• Add an option to set the tileset's attribution

Line simplification crash fix and disk space warning

• Fix a line simplification crash when a segment degenerates to a single point
• Warn if temporary disk space starts to run low

Add --drop-polygons option

• Add --drop-polygons to drop a fraction of polygons by zoom level
• Only complain once about failing to clean polygons

Fix build problem (wrong spelling of long long max/min constants)

• Fix build problem

Layer names independent of filenames

• Add an option to give specific layer names to specific input files

Long options and more careful memory allocation

• Remove temporary files that were accidentally left behind
• Be more careful about checking memory allocations and array bounds
• Add GNU-style long options

Be more careful about polygon splitting

• Don't get stuck in a loop trying to split up very small, very complicated polygons

More polygon fixes

• Increase maximum tile size for tippecanoe-decode
• Incorporate Mapnik's Clipper upgrades for consistent results between Mac and Linux
• Claim vector tile version 2 in mbtiles
• Split too-complex polygons into multiple features

Parallel processing of streamed input, tests, and other misc improvements

• Bug fixes to maxzoom, and more tests
• There are tests that can be run with "make test".
• Feature properties that are arrays or hashes get stringified
  rather than being left out with a warning.
• Make clipping behavior with no buffer consistent with Mapnik.
  Features that are exactly on a tile boundary appear in both tiles.
• Parallel processing of input with -P works with streamed input too
• Error handling if unsupported options given to -p or -a