manpage: fix typo
lua: add youtube-dl hook script

This merely adds the file without using it, for the sake of retaining
authorship information.

Signed-off-by: wm4 <wm4@nowhere>
player: integrate ytdl_hook.lua
input.conf: add some additional bindings
manpage: changes.rst: add youtube-dl script
options: add --ytdl-format option for youtube-dl format

It's passed with the '--format' option to youtube-dl.

If it isn't set, we don't pass '--format best' so that youtube-dl can
use the options from its configuration file.

Signed-off-by: wm4 <wm4@nowhere>