fp-ts backports

[samhh]

Some stuff that can potentially be dropped here:

• tap
• mapBoth

Additionally some new aliases:

• flatMap for chain
• mapError for mapLeft

[stefanoCrmg]

#185 should partially solve this issue.
I did not remove any of the mapBoth as they were not released with [email protected].

Is there any of function that you think would be a good fit for being made dual? https://github.com/gcanti/fp-ts/blob/master/src/function.ts#L773

Ideally I guess it would be great to have everything as dual but I'd say that maybe converting all of the unsafeUnwrap functions could be a good starting point?

[samhh]

I'm not personally interested in supporting data-first. It's not how I'd advise anyone to write functional code and it harms maintainability here. Open to other perspectives.