WARNING
this is a very rough script.
I have't tested complete building process.
it has no error checking, I'll fix it at some point.
currently it's just checklist/guide for how to create these images.


FOR OrangePi zero (LTS 512MB)
(sun8i-h2-plus-orangepi-zero)


By default script builds 1gb sd card images with small u-boot partition and
one big btrfs partition with compressed files. 
After image it built, you can dd image to your sd card, resize dos parition 
and run `btrfs filesytem reize max /` after orangepi booted.

===KERNEL CONFIG===
Script builds linux kernel out of mainline kernel.
it supports ext4, btrfs and f2fs. 
Config itself is quite minimal, you may need to tweak it to fit your requirements.
IT DOES NOT SUPPORT WIFI. afaik It's supported only by legacy sunxi-linux-3.4

I've had success creating image out of:
	stage3-armv7a_hardfp-20200509T210605Z.tar.xz
	linux-5.4.77.tar.xz
	u-boot revision 832bfad7451e2e7bd23c96edff2be050905ac3f6

you should use up to date verisons, these are just in case something breakes in the future.

script also tweaks some settings, you can edit them in syssetup()
script also requires portage-latest.tar.xz to be placed in `pwd`