Add "Enter to send" option

A user on the iOS App Store writes:

I want to love this app... I really do. It looks great and my home server runs with no hiccups at all. It’s solid. However on the iOS app there is no way to enable “hit enter to send”. As I use my ipad most of the time... with a connected keyboard case... this is a MAKE OR BREAK feature. If a Dev sees this and there is an option somewhere, please reply!

This seems like a very reasonable feature to implement and stick in the settings, although we should continue to default to requiring pressing the send button to send.