Should the specification live in parity_scale_codec docs?

[jsdw]

Just a thought; I feel like it would be good to have a form of the specification actually as part of the rust docs for the parity_scale_codec crate. Aside from keeping the docs coupled with the code implementing it, it would allow us to have doc tests to actually verify that all of the examples of encoding and decoding the various types are correct. I'd personally be quite happy to work on this if it was desirable.

Then, this page could focus more on the use cases and "higher level" things which involve making use of the specified bejaviour in various placea and whatever.