ship typings with npm package

[Uzlopak]

Fixes #435

[voxpelli]

Shouldn't the wreck options be imported from that module rather than duplicated here?

[Uzlopak]

@hapi/wreck ships with its typings.

[voxpelli]

@hapi/wreck ships with its typings.

My bad, I remembered it as if @types/simple-oauth2 were referencing @hapi/wreck's types, but I see not that they didn't.

Still – since this module has @hapi/wreck as a dependency, a distinct advantage over @types/simple-oauth2 would be to make use of those types then :)

[jonathansamines]

Hey @Uzlopak thanks for these changes. I am not well versed in typescript typings, so I am inclined to merge your changes and publish a new major, and then refine if necessary. Any chance you could target these changes against develop?