Merge the contents of docs user guide and quick start
The two documents are similar with only a few minor differences, where user guide(tubemq_user_guide.html) has been removed from the menu and we can merge it.
Update start/stop service commands
After TUBEMQ-172 patch, we have a simplified script for the start/stop service.
Fix demo example
The current demo example has an error and it won't work properly, so we have to fix it.
Improvement
Major
