pnmquantall
Run `pnmquant` on multiple files at once such that they share a common colormap.
TLDR
Run pnmquant on multiple files with the specified parameters, overwriting the original files
$ pnmquantall [n_colors] [path/to/input1.pnm path/to/input2.pnm ...]
Save the quantised images to files named the same as the input files, but with the specified extension appended
$ pnmquantall -ext [extension] [n_colors] [path/to/input1.pnm path/to/input2.pnm ...]
