L.BingLayer: fixes / updates / refactoring

[johnd0e]

Options:

• fix culture option for updated imagery sets
• fix minZoom / maxZoom options, add applyMaxNativeZoom method/option
• support style option
• support detectRetina option
• options are now compatible with https://github.com/digidem/leaflet-bing-layer

Constructor:

• key can be included in options

Misc updates and refactoring

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This change is 

[johnd0e]

@brunob

I've finished all planning changes here. Please check and merge, if you are interested in L.BingLayer. If not - just tell me, and I will setup dedicated repo.

[brunob]

Thx @johnd0e 'im totally intersetd in Bing layer, i'll check this asap :)

About dedicated repo, since many years i'm thinking about put every single script here in a dedicated repo, maybe it's the time to do it for Yandex first. We could do that in a common organization. Maybe @leaflet-extras could be the right place.

[johnd0e]

maybe it's the time to do it for Yandex first.

Ok, I will notify you when I finish with Yandex.

Maybe @leaflet-extras could be the right place.

I like this idea.

[johnd0e]

'Aerial* ' and deprecated imagery sets in fact do not have tiles for high zoom levels. And there is no reliable way to get real maxZoom value via API (we always get 21). So I've just implemented heuristic one (will commit after testing).

[johnd0e]

Ready for review

[johnd0e]

Could this be used for this point ?

Unfortunately docs are wrong here, and we never get error with zoom in range 1..21.

[brunob]

'k, let's merge it :)

[johnd0e]

One more note.

• Now we check max available zoom level on layer add.
• For some applications it'd more appropriate to check that continuously. It's not hard to implement it, but I doubt that it should be done in L.BingLayer itself, as everyone may implement it in own code (using provided applyMaxNativeZoom).

[brunob]

Nice, thx for that work @johnd0e !