Lukas Jezek authored Apr 27, 2020 and Tomas Krizek committed Oct 26, 2020

This change allows map() to work with systemd integration.

As a bonus the new client implementation is based on Lua cqueues
allows caller to wrap map() in worker.corroutine() and get
asynchronous execution/avoid blocking main loop.

Currently socket communication does not employ timeouts so a hang
instance will lead to hang map() call. This does not affect query
processing _if_ map() is being run in worker.corroutine.

Fixes: #554
Fixes: #620