Make sure all values in the `tiles` table or view are correct:
* zoom_level is between 0 and 30 (max allowed zoom)
* the x,y values are within the limits for the corresponding zoom level
* the column type of z,x,y are all integers
* the `tile_data` is a NULL or a BLOB
# MBTiles
* New `--agg-hash (update|verify|off)` flag replaces
`--update-agg-tiles-hash` (still supported, but not shown in the help
screen). This allows bypassing aggregate hash validation entirely,
without either updating or validating it.
* Simplify MBTiles SQL generation
* MBTiles now uses faster `1 << zoom` everywhere, and a dedicated TMS
inversion fn
* split up metadata insert and delete into separate fn
* consolidated schema initialization
* ensure db settings (like pragma) are always reset on new files
# Other
* Always sort JSON-serialized keys for consistency
* this affects `/catalog` key ordering, but content is the same
* Minor code cleanup
