Add content and latlng while initializing of Popup / Tooltip

[Falke-Design]

DivOverlay (Popup & Tooltip) supports now content in the options:

L.popup({content: 'Test'});

instead of

L.popup()
    .setContent('Test')

---

And it is now possible to pass an latlng point and the options as second parameter while creation:

var popup = L.popup(latlng, options?).addTo(map);

instead of

var popup = L.popup()
    .setLatLng(latlng)

---

This two new things together makes the usage of standalone popup / tooltip easier:

L.popup(latlng, {content: 'Test'}).addTo(map);

[johnd0e]

I see here some unrelated (but useful additions). Wouldn't it be better to open separate PR for them?

[Falke-Design]

Both makes the useage of popup and tooltip standalone easier, this is theier relation

[johnd0e]

this is theier relation

I expect relation to subject, which is defined it PR's title.

[jonkoops]

@Falke-Design do we want to keep this in the 1.9 milestone or can we move this forward? I'd like to start working on a release.

[Falke-Design]

@jonkoops it only needs a review from another maintainer like many other PRs. If you could do the review it would be great