vz 亚尔
示例用法：
var Yarr = require ( 'vz.yarr' ) ,
walk = require ( 'vz.walk' ) ,
yarr = new Yarr ( ) ,
result ;
walk ( function * ( ) {
result = yield yarr . pop ( ) ;
console . log ( result ) ; // Hello world!
} ) ;
walk ( function * ( ) {
yield yarr . push ( 'Hello world!' ) ;
} ) ;
