Working on system cron job triggered by users requests.
log cron job
Changed to make the limitation variable configurable.
Added DB storage based lock mechanism.
Merge branch 'develop' of https://github.com/harryxu/shanhaijing into develop
Added Facade pattern for using Lock class.
Capsulate cron run procedure into a class so that it can be invoked by other class or service .
fixed typo and make may_be_available method to be protected in class DBStoreLock
Add a new command 'cron'; Give function run a force option and return a status to indicate run or not.
removed unused namespace.
Completed email notification.
add a todo comment to email notification.
[email notify] not limited to notification type.
add a migration for creating new table semaphore.
Modified Cron static class, set more time for php execution, changed the first time of checking last cron run date time default value from zero to null.
fixed typo, syntax error.
In order to display html page to users without delay caused by cron run execution, moved cron execution to system event 'finish' and added ob_flush to send all html codes to users browsers.
Merge pull request #2 from jeffxu/develop

Run cron execution triggered by user requests and added emailing notification cron handler.