Improvements

First of all thanks for developed this useful plugin.
In my case I have encountered unfortunately some issues, for example if in a form there is a select or an option field, when export the sumbissions these fields are exported serialized.
Another issue is file fields are not supported.

I tried to make this improvements and I released a version on GitHub at link:
https://github.com/fabriziopera/contact-form-submissions

If you find this improvements usefully, I suggest to you to release an update with this bugfix.

Thanks for all.
Best Regards,

Fabrizio Pera