[enhancement] make modifier field optional

[VuiMuich]

.. so it isn't necessary anymore to have awkward empty values in the config.

[SergioRibera]

What do you think about having a default_modifier as a parameter in the configuration and only use it when no modifier is assigned to the keybind?

[VuiMuich]

That would make it impossible to assign keybinds like Brightness buttons etc. to work without the need of a modifier.
But you gave me a great idea: keybinds could be reorganized so the are grouped by the subset of modifiers. So this would almost feel like keymap layers. I'll try to come up with an example later.

[SergioRibera]

I was trying to make a contribution with the idea that I gave you, here I leave it more exemplified, although I would like you to explain me better your idea, it sounds great and maybe I can contribute in some way.

Config(
    default_modifier: ["Mod4", "Shift"],
    keybinds: [
        Keybind(
            command: Execute("st -e htop"),
            key: Key("x"),
        ),
        Keybind(
            command: Executes(["st -e htop", "st -e bpytop"]),
            key: Keys(["x", "m"]),
        ),
        Keybind(
            command: Chord([
                Keybind(
                    command: Execute("st -e htop"),
                    modifier: Some(["Mod4"]),
                    key: Key("c"),
                ),
            ]),
            modifier: Some(["Mod4"]),
            key: Key("c"),
        ),
    ]
)