* refactored from procedural to OOP
* updated ongoing maintenance windows to PagerDuty REST API v2
* update create maintenance windows to PagerDuty REST API v2
* update absent maintenance windows to PagerDuty REST API v2
* update pager alert module to PagerDuty REST API v2
* removed basic HTTP authorization
updated parameter description and examples
* fix failed sanity checks
* revised documentation according to review
* make obsolete service key parameter an alias to a new integration key parameter
