decoderWithIgnore

    pub fn decoderWithIgnore(ignore_chars: []const u8) error{InvalidCharacter}!DecoderWithIgnore {
        var ignored_chars = StaticBitSet(256).empty;
        for (ignore_chars) |c| {
            switch (c) {
                'A'...'Z', 'a'...'z', '0'...'9' => return error.InvalidCharacter,
                else => if (ignored_chars.isSet(c)) return error.InvalidCharacter,
            }
            ignored_chars.set(c);
        }
        return DecoderWithIgnore{ .ignored_chars = ignored_chars };
    }