- update mkbootimg: AOSP commit 147b355bb34cbd457a260c585be93193cef43b8e
- migrate all code from groovy to kotlin
- support DTBO and header_version, resolve#12
- upate README.expert.md too
- support AVB
remove original abootimg by Gilles Grandou <gilles@grandou.net>
create groovy abootimg and mkbootimg
previous bootimg.cfg moved to bootimg.json
update doc: README.expert.md