Add option to use default terminal colors

[augustotx]

Title says it all, but

Right now I can only assign colors to a theme by declaring them with hex codes or rgb values. I didn't find any option to not declare a theme and use the default terminal colors when initializing tuile.

Could look like something like this

pub fn customTheme() tuile.Theme {
    return tuile.Theme{
        .text_primary = tuile.Color{ .default = .text },
        .text_secondary = tuile.Color{ .default = .text },
        .background_primary = tuile.Color{ .default = .background },
        .background_secondary = tuile.Color{ .default = .background },
        // and so on...
    };
}

I'm currently writing a vim clone to learn zig and I would love if tuile could look like this!

also,

Thank you for making tuile, it's amazing!