Towards 1.13

[xoft]

If you're looking for the minimum amount of changes, #4274 is the minimum required to connect and render.

That's too minimal (no palette at all yet). And I think we need to do the Flattening as well, on the internal block representation.

Could future versions simply extend from the 1.13 palette?

Not necessary, the (network protocol's global) palette is represented in a data file that is generated from the server, we won't need to write anything to support newer versions in this regard, just add a new data file.