Make create_event_handlers method private, update guard
Add initial work on accepting natural language time ranges

Add:
 * Chronic gem for natural language time recognition
 * Two new methods for processing process_since and process_between (
   of which is still a huge WIP)
 * Two new rake tasks for debugging process_since and process_between
 * Smart logic on CLI for delgating processing to the correct method
   based on parameters