0.15.0

• Do not leak corrupted volumes when GrootFS is killed half-way during a grootfs create.
• Uses a more user-friendly error in grootfs delete when the image is not found.
• Apply a consistent configuration file options naming convention.
• Remove the need of passing --xfs-progs to grootfs stats in the overlay-xfs driver.
• Allow newer layers to overwrite existing files with symlinks.
• Always create the whiteout device when using the overlay-xfs driver.