Update to 2.6.8
    
    - Quote the tables for the key and mouse bindings in the README.md as code
    - Do not hardcode the list of useful m17n input methods
    - Use LOGGER.exeption() in exception handlers
    - Use python logging module with log file rotation instead of writing to stdout/stderr
    - Fix set_preedit_underline() with parameter update_gsettings=True