`howl`: cli arg to set a stop time

[rerpha]

I would like howl to optionally set a stop time, and not send a run stop. the stop time field of pl72 can be used for a run with a defined run time.

[rerpha]

this will only work with frames per run (or whatever the argument is to keep sending run stops/starts) to 0 or whichever value is used to only send 1 run start