Adding config to directly dismiss from long form

Description

I want to add feature to dismiss modal directly from long form. Currently, if I swipe to dismiss in long form state, the modal height stops in short form state. I know that in sample code, UserGroupViewController has feature to dismiss directly from long form height. Therefore we could write much better by using this feature. I want to add config value to manage this.

and I already have made pull request. I hope this feature would be accepted. https://github.com/slackhq/PanModal/pull/124

What type of issue is this? (place an x in one of the [ ])

• [ ] bug
• [x] enhancement (feature request)
• [ ] question
• [ ] documentation related
• [ ] testing related
• [ ] discussion

Requirements (place an x in each of the [ ])

• [x] I've read and understood the Contributing guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [x] I've searched for any related issues and avoided creating a duplicate issue.