Move MCRegionFile to its own source file.
Remove knowledge of chunk structure from MCRegionFile. Rename loadChunk to readChunk.
Remove compress, decompress, unload, isLoaded, compressedSize methods.
Remove compressedTag, dataIsPacked, loadedChunkQueue/Limit, decompressedChunkQueue/Limit members.
Rename InfdevChunk to AnvilChunk. Keep in place the conversion to old-style chunks until all client code is updated.
Remove most checks for self.version and keep only the VERSION_ANVIL code in place
Rename Alpha tests to Anvil tests.
Change several tests to load the AnvilWorld test data.
Change ZipSchematic test to export an area from the center of the world instead of from hard-coded coordinates.
