anvil_blockdata.py raise a ValueError

[psolyca]

When you try the example anvil_blockdata.py with a existing data array in a *.mca file, the following error raise in the print_chunklayer function:

ValueError: byte must be in range(0, 256)

Cause when a data array exist, the blocks array should be a short integer and not a bytearray anymore.
I fix it like this (do not forget to import array):

def print_chunklayer(blocks, data, add, yoffset):
    blocks = array.array('h',blocks[yoffset*256:(yoffset+1)*256])
    data = array_4bit_to_byte(data[yoffset*128:(yoffset+1)*128])
    if add is not None:
        add = array_4bit_to_byte(add[yoffset*128:(yoffset+1)*128])
        for i,v in enumerate(add):
             blocks[i] +=  256*v

    assert len(blocks) == 256
    assert len(data) == 256

     for row in grouper(zip(blocks,data), 16):
         print (" ".join(("%4d:%-2d" % block) for block in row))

[macfreek]

Fixes with pull request #84.