Add failure image to test object

The main motivation for this is when there is a test failure, I would like to
easily grab the path for the failed test image. I then take the failed image
and post it to a url for others to see. This simple change allowed me to easily
do that.
Add config flag to cleanup comparison images

The motivation behind this is I do not want to keep the comparison images
around, all I really care for is the failure images. Also I wanted a solution
that works in parallel.
fixed link in readme
Merge branch 'add-failure-image-to-test-object' of https://github.com/BaseInfinity/PhantomCSS into BaseInfinity-add-failure-image-to-test-object
Merge branch 'BaseInfinity-add-failure-image-to-test-object'
Merge branch 'add-config-setting-to-cleanup-comparison-images' of https://github.com/BaseInfinity/PhantomCSS into BaseInfinity-add-config-setting-to-cleanup-comparison-images
Merge branch 'BaseInfinity-add-config-setting-to-cleanup-comparison-images'
bump and readme