Filename prepends in load_tif_from_directory

[adamimos]

The filename_prepend input should be changed to automatically include the './' and the '*', so that if the user wants all the files they just type load_tif_from_directory('','downsample','preprocess')

[achristensen56]

idk if it should automatically include the ./, I think users will be used to supplying that for directories, and we might end up with a lot of ././ cases...