Support for modifying the runas user

[jarosser06]

Its generally not a good practice to run applications as a privileged user so there should be a user option that allows pm2 to be run as that user.

[miguelcnf]

I agree - afaik pm2 has 2 ways of doing this:

• starting as the current shell user (start actions)
• starting as the user specified in the init script (startup action)

Neither is based on the configuration file schema tho.

We'll want to cover both scenarios.

[jarosser06]

I have a PR incoming for this.

[jarosser06]

Added in #5

[miguelcnf]

Merged and released in 0.3.0.

Thanks! :)