Add a more powerful postprocessor script

[404Wolf]

I wrote a more powerful script for computing a bounding box and cropping. My new script requires passing -c to reSnap, and there currently isn't a way to add extra args, to get the best effect. This is because reSnap automatically does some color adjustments that are very lossy. I'm working on rewriting the plugin to some extent to conform to the newer obsidian API and clean things up a bit, and I'll add the ability to specify arguments.