BN: play
SF: play.c
SN: list of commands
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-N: pause
-D: Stop playing.
-U: pause
-H: When paused, it is still possible to jump around in the file via the jmp and ff
-H: comands.
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-N: tasks
-D: Print list of active tasks.
-U: tasks
-H: Mainly useful for debugging.
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-N: quit
-D: Exit para_play.
-U: quit
-H: Pressing CTRL+D causes EOF on stdin which also exits para_play.