Minimize calling `.data._shmarray.attach_shm_array()` as much as is
possible to avoid the crash from #332. This is the suggested hack from
issue #359.
Resolves https://github.com/pikers/piker/issues/359
Define the flows table as a class var (thus making it a "global" and/or
actor-local state) which can be accessed by any in process task. Add
`Fsp.get_shm()` to allow accessing output streams by source-token + fsp
routine reference and thus providing inter-fsp low level access to
real-time flows.
Tyler Goodlet