6.0.0a
* Add CRC to Settings making future upgrades more fail-safe
* Remove version 3, 4 and pre 5.2 settings auto-upgrade. See
https://github.com/arendst/Sonoff-Tasmota/wiki/Upgrade#migration-path
* Change default CFG_HOLDER from 0x20161209 to 4617 (=0x1209) - no
impact on default upgrades