Implement sending transactional messages with required and optional parameters

Largely, this is to support new arguments: 

```
   reply_name	Name for 'Reply-To' email field, defaults to 'from'
   from_address Email for 'From' email field, defaults to 'reply_to'
```

See: https://expresspigeon.com/kb/transactional-send

Adding a second method makes sense because a number of arguments are running out of control. 
