code: function GraphBuilder(options){
  
    options = options || {};
  
    // Precedence for resolvers.
    this.resolvers = options.resolvers || [
      require('./resolvers/absolute'),
      require('./resolvers/relative'),
      require('./resolvers/environment')
    ];
  
    this.handlers = options.directives || [];
  }
docs: Instantiate the GraphBuilder with the set of Directive Handlers.
  
  Directive Handler:
  {
  strategy: 'name',
  handle: function(DirectiveContext, tree, metadata, callback){
  return callback(err, DirectiveContext);
  }
  
  @param options {Object}
  @constructor