Session locking for File storage

[nebulousGirl]

I know the current File storage does not support session locking. I implemented my own File storage with session locking for concurrent requests in my project.

Is it something that you would include natively within this package? If so, I can submit a pull request.

Would you create a new storage FileLocking or include it inside File with an option to enable or disable?

[msarca]

I believe that a new storage class would be the ideal solution at this point. Please send PR