Permissive wrapping, fix global pollution and export types

Adds permissive wrapping of the fetch function while retaining the original typing of the wrapped library. This enables us to handle that there are slight variations between fetch implementations in node.

This change also removes the need for the triple-slash directive which polluted the global namespace with DOM typings. The new version also exports all the types defined in the library for good measure.

Many thanks to @alecmev for providing an excellent PR which made these changes possible.