Add multiple users support

In order to support multiple users support, modify the client and config
struct to support this functionality
Add config and config example file
Merge branch 'master' into dev
Merge branch 'master' into dev
Fix multiple user test issue
Update README.md
Update README.md
Merge branch 'master' into dev
Add delete file support

Support delete one file with multiple users and tasks
Merge branch 'master' into dev
update README.md
correct item number of readme.md
Fix list file bug

Task count for list file is wrong, fix it
Merge master modification
Fix bug of update config
Fix update config file 0 length error
merge readme from master branch
Add delete all files functionality

Add the method DeleteAllFiles to PolarisClient to support delete
all files in batch mode. Has tested with devint
Update readme to synch with functionalities
Fix delete all files async issue

1. Fix delete all files async issue for different users
2. Add limit CLI option for list files