Enhancement: Support multiple file selection

[JarrydLong]

Is your feature request related to a problem? Please describe.
In some use cases, you might not need or want to create multiple file fields in order for users to upload their example work (for example).

Describe the solution you'd like
Be able to set a 'multiple' => true when setting up a file field. Maybe a 'maximum' limit too so that visitors can't add crazy amounts of files.

Describe alternatives you've considered
Create multiple file fields.

[greenhodge]

Upvote!