v4.0 - todo

[jonschlinkert]

• Support config comments
• Add process.on('exit', ...) event to ensure that the user's "original" package.json is not changed if an error occurs.
• support flags for automatically linting, installing, cleaning, etc.
• support add for adding patterns for directories or files to include, and ignore for files to ignore, and allow -D or --devDependencies to be used with those commands.