Feature
* feat(flysight2csv): new cli, merge files, valid_offset flag
* rewrite CLI and separate argument parsing from program logic
* also merge reformatted SENSOR.CSV and TRACK.CSV files into a MERGED.CSV
* add valid_offset flag to reformatted files (False if datetime is invalid) ([`a881dd4`](https://github.com/yoleg/flysight2csv/commit/a881dd4eb7ca02a491d266d5b5bd2745fa9b3f58))