new NCBI Nucleotide web translator

Using the Entrez Eutils JSON API. This is a translator for datasets, and therefore has some limitations, e.g. apparently no author information.
* Because you might be throwing out items here, you should not return `true` for `checkOnly` above. It's possible (though probably unlikely on NCBI) that in `doWeb` you would end up with no items here.

* If the match succeeds (i.e. `id !== null`) the value you're looking for is actually `id[0]`, not `id` in `items["" + id]`

* You're sort of on the right track for storing the id in the items object by prefixing it with a string. This is mostly necessary because of [Chrome being stubborn and refusing to treat numeric properties as all the other properties, which messes up the ordering](https://code.google.com/p/v8/issues/detail?id=164), but from what I understand, simply converting the id to a string is not enough, so you want to prepend it with something (though suffixing should work too), e.g. `"_" + id[0]` You would then have to trim that off later.

* Use `ZU.trimInternal(title)` to get rid of any superfluous spaces in the HTML.