Pretty yaml

[macisamuele]

As exists pretty-format-json I have added an equivalent hook for yaml files.
Since formatting of yaml files is heavily dependent on parameters passed to yaml.dump method I have decided to expose all the yaml.dump kwargs parameters in order to let the users of the hook to decide how a pretty YAML file looks like!

[asottile]

yaml isn't round trippable so this hook isn't valid -- at best this will work for things which have no comments and no human decided formatting. At worst this will be a constant frustration for anyone trying to add comments / lists formatting / refs / any of the other features of yaml in the 72 page spec.

You can see (struggled) attempts to implement something like this: pre-commit/pre-commit#211 pre-commit/pre-commit#415

[macisamuele]

@asottile++ I wasn't thinking about comments ... I'm closing the PR!

[asottile]

<3 we've tried making this, and ran into the same things (why it doesn't exist!) :D