Support for Validating multiple files.

[rexfordnyrk]

Hello,
Thanks for the great package. the docs say only one file validation is supported.
Are there plans for doing multiple file validations for fields that have multiple files? If not will you accept a pr for this? I am willing to get that done. I see your code relies on the request.FormFile which only does return the first file for the key in the request.
could we not just implement something more robust to make room for multiple files with the same key?
Do let me know what you think.