Release v2.3.1

@alitto

Pull requests

fix(pool): avoid race conditions when a task is submitted while the pool is stopping by @alitto in #105
feat(pool): add non-blocking submission methods and dropped tasks metric by @alitto in #107

Ensure closed atomic bool is toggled and checked while holding the mutex to avoid race conditions.
Ensure workersWaitGroup.Add() is always called while holding the mutex to avoid race conditions.
Improve comments on submit methods to clarify the behavior when the pool is stopped.
Refactor trySubmit method to make it simpler and more clear.
Centralize worker launch in a new method called launchWorker.
Replace subpoolSubmit with subpoolWorker method.
Add methods to submit individual tasks in a non-blocking fashion (TrySubmit and TrySubmitErr). Requested in #103
Expose new DroppedTasks metric that reflects the number of tasks that were not executed because the queue was full. Issue reported in #100
SubmittedTasks metric now includes dropped tasks and it stops being updated once the pool is stopped.

Full Changelog: v2.3.0...v2.3.1