add hyperlinks to documentation and clarify derive macros

[lolbinarycat]

this makes it easier to navigate the documentation.

one comment seemed to suggest that the reexport of the derive macros was depricated, however that has been ignored for several reasons:

1. exposing macros through a derive feature flag is common practice, see the serde crate for an example.
2. using a feature flag means you can't accidentally have a version mismatch.
3. the reexport is used in several examples
4. the only evidence of deprication is a private comment, which would never be seen by normal users of the crate.