This as a rewrite of `gammu_get_unread_sms.py` script that adds:
- Support for long SMS
- Added proper CLI interface (see --help)
- Added optional --delete parameter which deletes SMS after printing them as JSON
- Added optional --show-read parameter which shows all not Unread marked SMS
- Added logging and --debug option
- Retain retrocompatibility with earlier versions of this script
- Retain retrocompatibility with Python 2.7+ (hopefully)
Fixes#181.
Btw, the interface with RaspiSMS could be improved with a temporary JSON file, using stdout seems lossy.