Added a method to convert a ztime into a ruby time object
Removed uneccessary instance variables
Refactored NLPQuery to not be a subclass of string, but encapsulate a
string

This allows greater control, reduces the size of the api used by
NLPQuery, and brought to light a few methods that really didn't belong
in NLPQuery (eg. interpret_time and interpret_date)
Removed legacy NLP#output
Added CHANGELOG.md