v2.1.0

• Allowing the log function to be overridden.
• Reworking log output as structured data.

v2.0.0

• Major refactor for configurability and testability.
• Adding test coverage with Mocha and Istanbul and configuration for eslint.
• Removing DKIM-Signature headers for the amazonses.com domain to prevent error
  when forwarding.
• Improving format of modified From header.
• Adding documentation and example for implementing this module.