- Correct filename
- Use consistent variable name throughout class
- Use a common log method for printing out the properties, so
  that we never print out the password regardless of how the pool
  was configured.
- Make HikariCPConfig a singleton (object) since it's behavior
  is completely different based on using a separate config file
  vs. using the Play configuration file.
- Update logging
- Use defaults similar to the default Play pooling configuration.
- Don't crash at startup with an NPE if non-mandatory configuration
  items are not provided and we're using Play for configuration.
- Update README to reflect the fact that this plugin does not
  work with Play 2.2.x without some minor changes.