Merge branch 'dev' into parallel
adds master_sched_allnode.py, who regardlessly put non-fixed jobs to every node
adds BaseJob.pop()
- adds QueueGroup
- stop-the-world during master's resucheduling
- example/02_FilterSplit works with allnode scheduler
- example/02_FilterSplit ** does not work ** with allnode scheduler
- all examples work with firstnode scheduler

Signed-off-by: Sho Nakatani <lay.sakura@gmail.com>
adds sleep_sec for istreams
- adds `fixed_to`
- found bug: example/02 w/ randomnode scheduler doesn't stop sometimes
Signed-off-by: Sho Nakatani <lay.sakura@gmail.com>
bugfix: correct finished_jobs collection (or is wrong, | is right)
bugfix: repeadedly produce `None` when local queue is empty, then infinite number of remote workers will be informed `empty`
use variable for example
launch istream only on 1 node without fixed_to parameter
Merge branch 'stop_the_world' into dev