Validates level and sets .le$log_level. Called internally by
SetLogger() methods and may be called directly when only the level (not a
logger object) needs to change.
Usage
SetLogLevel(level)
# S3 method for class 'character'
SetLogLevel(level)
# S3 method for class 'loglevel'
SetLogLevel(level)
# S3 method for class 'numeric'
SetLogLevel(level)
# Default S3 method
SetLogLevel(level)