Add "-exitafter" parameter in continuous "from-kafka" sync

[philrz]

For the continuous sync (#83) that's currently a work-in-progress in the from-kafka-continuous branch, a user has expressed the following requirement:

I need [a flag] with zync from-kafka in the branch from-kafka-continuous
This [value for the flag] will be [a time value] and it will stop zync process. It needs to force zync to reload a new YAML file.

[nwt]

#94 adds an -exitafter flag to zync from-kafka.