Revert commit f7fde54, which reintroduced tiling issues fixed by 9231133.
- Add --png8 argument to quantize 32-bit RGBA to 8-bit RGBA paletted PNGs.
- Specify NUM_THREADS option for gdal_translate to use all CPUs
- Update MANIFEST.in to include required files
- Add support for Python 3.5 and 3.6
- Replace vipsCC with pyvips
- Use pytest and tox for testing
- types.py has been renamed to gd_types.py to avoid import conflicts
- Remove multiprocessing as it creates noise in mbtiles output files with
pyvips and doesn't appear to have a significant impact on processing speeds