Allow to import hyper-ts without es6 or lib directories

[mlegenhausen]

With the introduction of the ReaderMiddleware we need to choose between es6 and lib directory for imports. As the rest of the fp-ts ecosystem support the import without these directories I think it is consequent to add it here too.

@DenisFrezzato do you have already something like this in the pipeline if not I can pick this up?

[DenisFrezzato]

No, I don't have anything in the pipeline on this topic, feel free to pick it up.