utils.log supports module reloading and recreating loggers

Calling create_logger will now:
- Destroy the named logger if it already exists
- reload the logging config
- Create and return a new logger using the latest config
- Actually use the max_file_backups setting (oops)

Also, you can specify settings for individual loggers
Merge pull request #364 from seandst/reloadable-logger

utils.log supports module reloading and recreating loggers