Additional event handling functionality

This changeset enables the following:

- Multiple independent events tied to the same RegEx
- Ability to have an event with no sound
- Ability to run an external application when an event is triggered

I made some changes to the XML Settings file structure for storing events; namely, I replace the RegEx key with a Guid, and moved the RegEx to an element, and I also introduced an Executable element. The LoadEventSettings() method still handles the original settings file and it will be migrated to the new format when SaveEventsNode() is called.

Note: You may want to discard the changes to the readme.