Merge branch 'master' into release-v0.2.3
Merge branch 'release-v0.2.3' into develop
Added Notifier to display messages for long lasting operations

* Added Notifier (a threaded message queue system)
* Implemented long lasting operation use Notifier
Merge branch 'release-0.2.4'

Notifier displays messages for long lasting operations

* Added SIGINT/SIGTERM handler to stop threads gracefully
* Added Notifier (a threaded message queue system)
* Implemented long lasting operation use Notifier
Changed version number