Sugarchain Yumekawa v0.16.3.21rc1

Changes:
[x] switch: genesis hash
[x] add: mainnet seeder

Fingerprint:

BB27 9FE1 59A0 E40E D02B  3365 B9DD BDE2 AAAD C421
cryptozeny (sugarchain developer) <[email protected]>

Credits:
Thanks to everyone who directly contributed to this release (alphabetical order)

cryptozeny
ilmango-doge
okoto-xyz
solardiz
volbil
zawy12