Add a data module

[linkmauve]

This is a measure for computer information, it goes down to bits but the internal value is the octet.

We decided against using the byte as the internal value because its size is architecture-dependent, on DSPs for example a byte could be 16 bits instead of 8 as it is usually understood. The octet on the other hand is always defined as eight bits.

This was done as part of the Cambridge Rust meetup.

[thejpster]

Thanks for this. I've pulled it into a branch before I send it upstream.