data.go: Use worldupgrader package for block upgrading and updated Dr… …agonfly version.
Merge remote-tracking branch 'origin/master'
go.mod: Updated to dragonfly v0.6.0.
data.go: Parse palette once instead of parsing blocks everytime in At… … to improve performance.
data.go: Fixed a bug where the wrong palette pointer was written when… … the palette was grown.
structure.go: Save the palette when Write is called.