主動驅動事件執行--createEvent

1. createEvent（eventType）
參數：eventType 共5種類型：
    Events ：包括全部的事件. 
          HTMLEvents：包括 'abort', 'blur', 'change', 'error', 'focus', 'load', 'reset', 'resize', 'scroll', 'select', 
                                    'submit', 'unload'. 事件
          UIEvents ：包括 'DOMActivate', 'DOMFocusIn', 'DOMFocusOut', 'keydown', 'keypress', 'keyup'.
                                  間接包含 MouseEvents. 
          MouseEvents：包括 'click', 'mousedown', 'mousemove', 'mouseout', 'mouseover', 'mouseup'. 
          MutationEvents:包括 'DOMAttrModified', 'DOMNodeInserted', 'DOMNodeRemoved', 
                                      'DOMCharacterDataModified', 'DOMNodeInsertedIntoDocument', 
                                      'DOMNodeRemovedFromDocument', 'DOMSubtreeModified'. 

2. 在createEvent後必須初始化，爲你們介紹5種對應的初始化方法
  HTMLEvents 和 通用 Events：
            initEvent( 'type', bubbles, cancelable )
    UIEvents ：
                      initUIEvent( 'type', bubbles, cancelable, windowObject, detail )
    MouseEvents： 
                      initMouseEvent( 'type', bubbles, cancelable, windowObject, detail, screenX, screenY, 
                      clientX, clientY, ctrlKey, altKey, shiftKey, metaKey, button, relatedTarget )
    MutationEvents ：
                      initMutationEvent( 'type', bubbles, cancelable, relatedNode, prevValue, newValue, 
                      attrName, attrChange ) 

3. 在初始化完成後就能夠隨時觸發須要的事件了，爲你們介紹targetObj.dispatchEvent(event)
    使targetObj對象的event事件觸發
  須要注意的是在IE 5.5+版本上請用fireEvent方法，仍是瀏覽兼容的考慮

4. 例子
    //例子1  當即觸發鼠標被按下事件
    var fireOnThis = document.getElementByIdx_x('someID');
        var evObj = document.createEvent('MouseEvents');
        evObj.initMouseEvent( 'click', true, true, window, 1, 12, 345, 7, 220, false, false, true, false, 0, null );
        fireOnThis.dispatchEvent(evObj);

  //例子2  考慮兼容性的一個鼠標移動事件
    var fireOnThis = document.getElementByIdx_x('someID');
    if( document.createEvent ) 
    {
        var evObj = document.createEvent('MouseEvents');
        evObj.initEvent( 'mousemove', true, false );
        fireOnThis.dispatchEvent(evObj);
    }
  else if( document.createEventObject )
  {
      fireOnThis.fireEvent('onmousemove');
  }