Support options object

[mweststrate]

For some relative dependencies, one might want to customize whether (or how) a build should be triggered, what paths should be watched, etc. So instead of just specifying a path string as dependency, it should also be possible to specify an object with several options. Example:

"relativeDependencies": {
  "dep": { 
    "path": "../", 
    "build": false, 
    "excludes": ["dist"] 
  }
}

[rifler]

maybe this config should be inside dependency?