Improve the System.Logger module

[emqplus]

How to define the following functions:

• [ ] logger:debug/2, debug/3
• [ ] info/2,info/3
• [ ] notice/2,notice/3
• [ ] warning/2,warning/3
• [ ] error/2,error/3
• [ ] alert/2,alert/3
• [ ] critical/2,critical/3
• [ ] emergency/2,emergency/3