It's not really great. But I think it's good enough to save someone
who's lost. Most importantly, it should become obvious _what_ the
console expects (input commands), and how to exit it.
Would be nice if we could show some documentation, or give a link to
documentation, but that's out of scope and/or not easy.
I considered implementing the "help" command as builtin command in
command.c. On the other hand, this could not show console.lua specific
help, so I implemented it in console.lua. The ad-hoc command parsing
(that sort-of mirrors mpv input command syntax) for the "help" command
is probably the worst part of this.