add onclick.js

Signed-off-by: arcticlion <david.malan@aol.com>
证明DOM0级事件处理程序是元素的方法

Signed-off-by: arcticlion <david.malan@aol.com>
删除事件处理程序

Signed-off-by: arcticlion <david.malan@aol.com>
add addEventListener.js

Signed-off-by: arcticlion <david.malan@aol.com>
write a Function of addEventListener in addEventListener.js

Signed-off-by: arcticlion <david.malan@aol.com>
write a Method of removeEventListener in addEventListener.js

Signed-off-by: arcticlion <david.malan@aol.com>