Unit = excerpt (.rezx export option for crowdsourcing corpus annotations)

[johnwdubois]

In the Rezonator export of a .rezx file, allow the user to specify that each unit should be an "excerpt". (This allows a user to create a corpus resource without having to use the stacker.)
One "cheat" to do this easily would be to first make every unit into a stack. But it would be better to allow it to be done directly from units. )
(One or more of these "excerpts" may be used to create a "stimulus" for experiments, or a "task" for corpus annotation.)