Adds --node-args command line option to pass options to node

This pull request attempts to address #45 - not being able to pass v8/node options to processes managed by pm2.

By way of example it lets you do this sort of thing:

```
$ pm2 start --node-args="--debug=7001 --trace-deprecation" script.js
```

Please let me know what you think.  I'm happy to discuss and make any amends required.