function relationship (list, path, options) {
	this.many = (options.many) ? true : false;
	this.filters = options.filters;
	this.createInline = (options.createInline) ? true : false;
	this._defaultSize = 'full';
	this._nativeType = keystone.mongoose.Schema.Types.ObjectId;
	this._underscoreMethods = ['format', 'getExpandedData'];
	this._properties = ['isValid', 'many', 'filters', 'createInline'];
	relationship.super_.call(this, list, path, options);
}
Relationship FieldType Constructor
@extends Field
@api public