- Removed the ability for the user to call Catamaran::LogLevel.default_log_level=.  This was confusing.  The user should just set the log level on the root logger
-  Reworked the backtrace mechanism so that loggers have their own backtrace_log_level
- Updated the README file
- Cleanup test cases
Catamaran::Logger#_log() becomes Catamaran::Logger#log()