Implement printf

[Vardan2009]

Untested implementation (needs improvements)

fn printf(fmt : ptr8, ::) : byte {
    ; fn_arg x (for accessing other arguments)
    let arg_idx : byte = 0
    loop {
        if *fmt == '%' {
            fmt = fmt + 8
            if *fmt == 'd' {
                printi(fn_arg arg_idx)
                arg_idx = arg_idx + 1
                fmt = fmt + 8
                continue
            }
            if *fmt == 's' {
                prints(fn_arg arg_idx)
                arg_idx = arg_idx + 1
                fmt = fmt + 8
                continue
            }
            if *fmt == 'x' {
                printx(fn_arg arg_idx)
                arg_idx = arg_idx + 1
                fmt = fmt + 8
                continue
            }
        }
        printc(*fmt)
        fmt = fmt + 8
        if *fmt == 0 break
    }
}