emit process:exception with the full err

Hello,

This PR exposes the "full" error on uncaughtException allowing seamless integration with already existing handlers. What do you think about it?

example
````
var ipm2 = require('pm2-interface')();

ipm2.on('ready', function() {
    console.log('Connected to pm2');
    ipm2.bus.on('process:exception', function(event){
        existingHandler(event.err);
    });
});