JOURNAL: Add support for summary(js, by = "future") #351

Job	Run time
future.batchtools (release)	4m 21s
future.callr (release)	2m 48s
doFuture (release)	3m 55s
future.apply (release)	3m 42s
furrr (release)	4m 18s
doFuture (release) multisession	4m 14s
future.apply (release) multisession	3m 53s
furrr (release) multisession	5m 13s
future.apply (release) keepWhere	4m 2s
future.apply (release) !keepWhere	3m 44s
	40m 10s

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