Add SQL functions to generate quadkeys

Makefile

databaselib/database.py

pyproject.toml

quadkeyfunctions/01a_clip.sql

quadkeyfunctions/01b_clip.sql

quadkeyfunctions/02_map_size.sql

quadkeyfunctions/03_latlon_to_pixel_xy.sql

quadkeyfunctions/04_pixel_xy_to_latlon.sql

quadkeyfunctions/05_pixel_xy_to_tile_xy.sql

quadkeyfunctions/06_tile_xy_to_pixel_xy.sql

quadkeyfunctions/07_tile_xy_to_quadkey.sql

quadkeyfunctions/08_quadkey_to_tile_xy.sql

quadkeyfunctions/09_quadkey_to_geom.sql

quadkeyfunctions/10_geom_to_quadkeys.sql

quadkeyfunctions/__init__.py

quadkeyfunctions/quadkeyfunctions.py

setup.py