Update manpage

The manpage at https://github.com/sharkdp/hexyl/blob/master/doc/hexyl.1.md currently seems quite outdated and almost untouched since 2022/release 0.12 and as such lacks several of the options, such as the Character/characters table for example.

In a perfect world, most of it would be generated from the code, but on a quick glance I didn't found obvious solutions for this, if any exist handling most of the task automatically.

I'm also unsure what's the Markdown flavor at use here, with things such as colons here and there?