v0.17.0

This is a major release fixing and improving many problems.

• Thread killers were replaced with one thread killer per as many threads as needed. It makes the threaded executor faster, slimmer, and simpler.
• Slave's process stderr is connected to the supervisor so it will have the chance to pipe its stderr in case of an unexpected exception in the slave's logic itself. The buffer was able to stall the slave's process because no process was cleaning its buffer. It is now configured to be unbuffered wishing it will fix the bug.
• There was a typo in threaded executor causing it to raise an exception after the completion of all the tasks.
• Requirements versions are now fixed
• Stop/Respawn can now be called in initialize/finalize

Breaking Changes:

• Worker config executor parameter was removed in favor of number_of_threads. See the documentation for how to choose the number.
• LogstashLogger was logging a "logger" field nested with name and level. These are now "name" and "level" in the parent document of the log.