Popup autoPanPadding with 4 padding parameters

[albburtsev]

At now autoPanPadding property is instance of L.Point and taken 2 padding parameters.
We need 4 padding parameters, for example autoPanPadding property can be instance L.Point or L.Bounds.

// Usage example
var rightTop = new L.Point(10, 20),
    leftBottom = new L.Point(30, 40),
    popup = new L.Popup({
      autoPanPadding: new L.Bounds(rightTop, leftBottom)
    });

If you approved this features, I'm ready write and send pull request.

Best regards.

[brandoncopeland]

I would find the feature helpful as well