chore: add typescript types

[oed]

This PR adds Typescript typings to this package.

Thanks to @carsonfarmer for creating these :) He has a great repo of types for ipfs related packages here: https://github.com/textileio/js-ipfs-lite/tree/master/src/%40types

[hugomrdias]

Thank you for your work, i will not merge this because we are do it in a slightly different, please read about it here ipfs/js-ipfs#2945

[oed]

Thanks @hugomrdias