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.