Add support for a filename format that allows one to specify the various parameters to the snap

[gdey]

Currently snap takes a lot of params, it would be nice to be able to have the filename state the params:

ie.

$ snap generate
 "[email protected],32.750000000000128,-117.250000000000000,32.500000000000000z12.5#3.0.jpg"

would be equalivent to:

$ snap generate generate --zoom=12 --bounds="-116.999999999999957,32.750000000000128,-117.250000000000000,32.500000000000000" --ppiratio=3.0 "[email protected],32.750000000000128,-117.250000000000000,32.500000000000000z12.5#3.0.jpg"