Cleaner output, more organized filekeeping

Made PhantomCSS more filesystem-friendly, keeping diffs and failure images in a specifed tmp directory, other than the main screenshots dir -- this makes it possible to keep baseline images in source control without polluting the source control with diffs and failures.

Also converted the original output to "verbose" mode, and made the standard output more CI-friendly by default.

Will add more later.  Thanks for doing the initial hard work of creating this tool!