WIP: Add standalone scanner

A simple standalone scanner application written in plain c so it can easily be cross-compiled for e. g. openwrt and similar, or built statically to run on a server.

The written file is almost a standard tsv file, just made a bit more compact with > and < indicating entering and exiting subdirs instead of full paths to avoid insane file sizes (and basic URL encoding since Linux is way too generous with allowed filenames).

I've tested the scanner and the parser, but kirigami doesn't work in general here so I haven't been able to test the whole thing.