Bernardo da Eira Duarte

I've configured my `fences.json` on my project and tried to add a unused dependency to see if it would warn. I've added `axios` and, despite it not beign used in...

Add a config option to filter events using expressions just like with the [custom messages filter](https://github.com/pankleks/pm2-health#filtering-custom-messages).

A simple jumpstart for the event filtering option. Fixes #21