Added new initializer to support a ForEach loop

[sverin]

The only init method available does not support a for each loop as the example below.

HPageView(selectedPage: $pageIndex) {      
    ForEach(images, id: \.self) { image in
        Image(uiImage: image.uiImage)
            .resizable()
            .scaledToFill()
    }
}

But this could be improved and supported by a new initializer

HPageView(selectedPage: $pageIndex, pageCount: images.count) {      
    ForEach(images, id: \.self) { image in
        Image(uiImage: image.uiImage)
            .resizable()
            .scaledToFill()
    }
}

[Lubakis]

This is a much needed feature

[fredyshox]

Release 1.5.0 (#18) will contain ForEach-like inits for HPageView and VPageView. It's a little bit different than this one, but it prevents from unintentional inconsistency of data passed to PageView and ForEach. So I'm closing this one.