Allow multiple -k <keycode> and -t <text> arguments

[patrickhpan]

#128 describes a usecase where one would want to call multiple -k or -t arguments for faster execution. Here's a quick fix I threw together to make this work!

[jamylak]

I've just tested this PR and it still works like a charm (edit: to be accurate I readded the code on my own local just didn't test this part

        if (synthesize_opt != 0 && option != synthesize_opt) {
            error("skhd: cannot pass arguments after -%c", synthesize_opt);
        }