v0.2.0

• Changed backup file name from package.bak.json to package.backup.json.
• Added incremental backup: package.backup.json, package.backup2.json...
• Added --backup, -b argument. It can now override config.
• By default backup is now true.
• Changed from deprecated optimist dependency to yargs. By using this dependency -h changes to --help and -v to --version only.