- switch to jsonpath-ng library to support more JSONPath features
- add support for row formulas as right side of row queries (making it possible to compare one column to another)
- add today() function for row formulas (today's UTC date in ISO YYYY-mm-dd format)
- add support for parsing Unix-style epoch timestamps (nanoseconds, milliseconds, or seconds)
- add long description in setup.py for PyPi (from README.md)
- work around xlrd date-handling bug (for malformed Excel dates)
- more cleanup on docstrings