Show Nim: New Pixie 5.0 release with significant performance improvements

[Butler_to_Cats]

My apologies for adding cruft that probably belongs on a separate thread.

Hey @oyster I suspect float values are used because **Pixie** is, at heart, a 
vector graphics library. That it also happens to handle pixel-based images is 
(somewhat tongue-in-cheek) almost incidental.

A slightly different approach?
    
    
    import pixie
    import pixie/contexts
    
    var bigImage = readImage("bigImage.png")
    var smallImage = readImage("smallImage.png")
    
    var bigContext = newContext(bigImage)
    bigContext.drawImage(smallImage, 10.0, 20.0)
    bigImage.writeFile("modifiedBig.png")
    
    
    Run

A big **thank you** to @treeform and @guzba for all their excellent work on 
Pixie.