ZFS autobackup v3 - TEST VERSION

New in v3:

Complete rewrite, cleaner object oriented code.
Python 3 and 2 support.
Backward compatible
Progressive thinning (via a destroy schedule. default schedule should be fine for most people)
Cleaner output, with optional color support (pip install colorama).
Clear distinction between local and remote output.
Summary at the beginning, displaying what will happen and the current thinning-schedule.
More effient destroying/skipping snaphots on the fly. (no more space issues if your backup is way behind)
Progress indicator (--progress)
Better property management (--set-properties and --filter-properties)
More robust error handling
Prepared for future enhanchements.