Drop `src` option

[sindresorhus]

It's an anti-pattern that libs accepts paths when the user can easily load it themselves. Some might want to load the file async.

[addyosmani]

Thanks for the feedback, Sindre. If you get a chance could you review the latest index.js to verify if all your suggestions have been incorporated?. Will tag a new release soon after if so :P.

[sindresorhus]

I added some feedback on the CLI PR and you shouldn't use process.exit in the lib code, it should only be used in the cli. Otherwise looks good.