System$getUsername: Retrieves the name of the user running R
Description
 Retrieves the name of the user running R.
Usage
## Static method (use this):
## System$getUsername(...)
## Don't use the below:
"getUsername"(static, ...)
Details
 First, this function checks the system environment variables USER,
 and USERNAME.
 Second, it checks Sys.info()["user"] for user name details.
 Finally, it tries to query the system command whoami.