This removes the "raw" man pages and converts them to Markdown, adding a build step using pandoc that converts them.
Having the man pages in Markdown makes them much, much easier to write and keep updated, at the cost of not having the raw formats easily available. Hopefully having the command to generate them in the Justfile will be enough.
It also splits out the EXA_COLORS environment variable into its own page, because it took up just under half of the one for the exa binary.
