Task Balancer Versions Save

1. hot update driver
2. hot remove/add driver

1. add new feature: remove destroy

Balancer::destroy($name);

1. If return false in beforeDriverRun hook can stop current driver.

1. 升级beforeDriverRun和afterDriverRun钩子，在其handler各自新加了$driver和$driverResult参数
2. 修改$driver->failed()为$driver->failure()
3. 修改Balacer::run()方法的参数为$name, array $opts

php 5.4 not support boolval() function, remove it!

update task hooks handlers arguments

upgrade hook handler`s arguments

upgrade hooks system. support multiple handlers for every hook!