StringIO#readlines

static VALUE
strio_readlines(int argc, VALUE *argv, VALUE self)
{
    VALUE ary, line;
    struct StringIO *ptr = readable(self);
    struct getline_arg arg;

    if (prepare_getline_args(ptr, &arg, argc, argv)->limit == 0) {
        rb_raise(rb_eArgError, "invalid limit: 0 for readlines");
    }

    ary = rb_ary_new();
    while (!NIL_P(line = strio_getline(&arg, ptr))) {
        rb_ary_push(ary, line);
    }
    return ary;
}