Shell Support + Fixes

• ✨added a new evaluator for shell scripts (see readme for more info)
• ✨ rules can be configured with match filters now
• 🐞 fixed a number of bugs relating to mute windows and alerts
• 🐞 fixed a bug for "yesterday" when used in time windows
• 💄 enhanced Slack messages to make things a little clearer and included resolution time with ongoing alerts when some are resolved