Libhxl

- 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

- allow selector for JSON data to be a JSON path as well as just a simple token
- add --selector option to all command-line scripts
- added toupper() and tolower() row functions
- fixed bugs with date heuristics and with JSONpath parsing of non-strings
- various code cleanup
- add a generic Makefile to simplify common testing and git tasks

* added optional encoding parameter to hxl.io.data() etc. to force a character encoding
* fix bug opening an Excel file when the server sends a
* content-type: zip MIME type
* fix bug peeking at UTF-8 files with many extended characters
* fix minor stability issues (e.g. unclosed file resources)
* fix CSV delimiter detection to ensure "," is always tried first

- added option to flatten multiple JSONPath results, separated by " | "

- significant improvements to Excel-file handling (even when the server sends a zipfile MIME type)
- fix bug peeking at UTF-8 files with extended characters
- fix CSV delimiter detection to ensure "," is always tried first
- allow forcing a character encoding in hxl.io.data()
- fix minor stability issues

Interim release:
* better error report when trying to open a zip file that's not an XLSX or zipped CSV