Horizontal margin between pages

[Valpertui]

Hello,

PR additions :

• Add of horizontalPageMargin setting, it defines how much space there is on each side of a page. ie 10 means for each page there is a 10pt margin on the right and left of each page, which means 20 pt between each pages. I'm not sure this name is the best one to describe this property.
• Update demo app to demo the horizontalPageMargin setting behavior. The scroll view must have clipsToBounds disabled and its width smaller than its superview for the margin behavior to show best how it works.

[evgenyneu]

Thank you @Valpertui, I am a bit busy right now, but I will have a look. I promise!

[evgenyneu]

Hi, @Valpertui, sorry for the delay. First I want to thank you for spending your time on this. But I do not think I want the margins in this library, sorry. I can see that your intention was to make the scrollview show a part of the next/previous images and that's great. The problem is that this simple change adds complexity to the library that I want to avoid. I intended to keep the Auk simple and focused so it can do few things and do them well. I know it is tempting to add features to existing product but we must always remember that new features make it more complex which in turn makes it less focused in accomplishing its initial purpose. You know, "less is more" philosophy.

I am sorry to reject your changes and hope you understand.