Case Style transformations in CharField

[jaimescose]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Hi! this is not about an issue, but a feature I would like to add to the existing CharField in order to support case style transformations.
The idea is to add from_case and to_case attributes when instantiating the field and transform the serializer representation.