Features
- Make plugin transport ZMQ multiplex (SkygearIO/skygear-server295)
This feature will enable the bidirectional plugin transport and multiplexing.
Calling `send_action` within the plugin will route back to the same worker
from now on. It is implicit, developer does not need to specific worker reuse
or not.
This merge also add dynamic threading at ZMQTransport.
It solved the problem of workers exhaust problem.
Bug Fixes
- Fix unable to set envvar to `false` (137)