May need to flip row coordinate

[tomalrussell]

Hi @ekfriis thanks for this, really useful to see a minimal example!

With my mbtiles file and a simple leaflet.js client, I needed to add a line in order to flip the y-coordinate

row = (2 ** zoom) - 1 - row

just before

flask-mbtiles/mbtileserver.py

Line 50 in ebadc1a

query = 'SELECT tile_data FROM tiles '\

so that tiles would render in right place.

I'm not sure if this would always be the case, or if it depends on how the mbtiles were generated. See https://gist.github.com/tmcw/4954720 for some discussion of XYZ vs TMS coordinates.