Documentation fixes

[tomato42]

A lot of documentation are comments, not documentation strings – they should be changed.

Most documentation strings don't actually document what the different arguments are and what the expected outputs are – using the sphinx format to document that would be nice.

Finally, many methods and functions are not documented at all, that should also be fixed.

[tomato42]

ecdsa module should also redirect people to keys, as that's where high-level API lives