Write Failed Image if Reference image not found

[ralfebert]

In case "Reference image not found" happens, it would be awesome if Snap.swift would write the Failed image.

[skyweb07]

Hey @ralfebert, thanks for the feedback, that could be a nice addition, the only problem that I see it's that when the image was not found it's that you are on test mode and not recording one so we might not expect to actually write the image

[ralfebert]

Hmm, I see the point. The context for this was that I added a few more image asserts to a test and I wanted to record just these images without overwriting the existing ones. And Snap write the images when a test is failing, so it would not come as a surprise (I don't mean they should be written in the folder for the reference images, just in the 'Failed' folder). Do you have any example where this would cause trouble?