add comments for orm and middleware packages.

Update README.md

Example:
peers = one;Two;Three

Update SessionExist to close the db connection

close the mysql connection

use connection pool for redis, support auto connection

fix #453

support redis cache auto connection

* this will support auto-connection

1. mysql fix last access time not update
2. mysql & redid Release when data is empty
3. add maxlifetime distinct Gclifetime

change a log

Error page improvements