"Edition mode"

[Manishearth]

Would be nice to have a mode where:

• It only applies edition lints
• It does this automatically, but prompts for approximate suggestions
• You can optionally ask it to apply idiom lints too

We can hardcode the list of edition lints and idiom lints

[Manishearth]

It occurs to me that for approximate suggestions we should spit them out after we've fixed everything else, so that if the user makes manual changes it's nbd. We should nail down a workflow here.

[ehuss]

I'm going to close as I believe this is mostly resolved by the --edition flag.