Support 's' format

[timolson]

I want to embed UUID's in my byte stream and used '16s' for that format, which is supported by struct, but netstruct complains about an unsupported format character. Other possible formats such as 'c' or 'B' return integers not a bytes object, which is what I need for deserialization back into a UUID. The only way I see to do what I want is to split my bytes by-hand and do partial parsing with netstruct and partial parsing on my own.