Better testing

[IdanHo]

Testing needs to be improved to cover more edge cases.

Regression testing for #99 can be implemented in the following ways:

• Nether chunks should be added to the test chunk dumps to test for correct skylight handling (bug 1)
• Improve cycle tests to make sure the raw dumped block and light (skylight and blocklight) buffers match and check the biomes match (bug 2 & 3)
• Chunks with more than 256 (2^8) different block states (aka, different block type or different block data) should be added to the test chunk dumps to test for correct global palette handling (bug 4)