Revamp logging configuration.

Revamp logging configuration.

* If --logging=none, tornado will not touch the python logging config.
* Colored output is optional.  If curses is not available or stderr is not
  a tty, non-colorized output will be used.
* Log output to stderr can be suppressed with --log_to_stderr=false
* Logs can be written to a file (non-colorized) with --log_file_prefix.
  Logs will be rotated, which can be controlled with --log_file_max_size
  and --log_file_num_backups.
* By default, logs go to a file if --log_file_prefix is set and to stderr
  if it is not.  To log to both stderr and a file, --log_to_stderr must
  be set to true explicitly.