Export derivations

[safareli]

In purescript derivations of some functions are exported from the module where typeclass is defined.

Currently we have then in readme.md as text, but having them exported from FL would be much better i think.

It will also encourage library authors to depend on FL as it could provide some helpful/tested derivations.

What others think on it?

[davidchambers]

I like this idea.

It's important to be clear that an algebraic data type must implement the various methods rather than rely on a library such as sanctuary-type-classes to provide derivations. Providing a lawful fantasy-land/bimap method, for example, does not satisfy the requirements of Functor. That said, it would be completely valid for the author of an ADT library to choose to derive the implementation of fantasy-land/map from fantasy-land/bimap. :)