Grid to mbtiles

You should reword ``Add the possibility of making MBTiles from files on the disk``, since we're talking about grids to mbtiles here. 

And squash the ``typo`` commit.

For this, you can do : 

    git rebase -i origin/master
    ...follow the instructions (replace pick by either squash or reword)...
    git push -f origin disk-to-mbtiles