input: Write a function named create_genesis_block that generates the first block in the blockchain. This function should initialize the first block with an index of 0, data as "Genesis Block", and a previous_hash as "0". Return the created block.
  assert create_genesis_block().index==0
  assert create_genesis_block().data=="Genesis Block"
  assert create_genesis_block().previous_hash==0
  assert create_genesis_block().hash is not None
output: def create_genesis_block():
      class Block:
          def __init__(self, index, data, previous_hash):
              self.index = index
              self.data = data
              self.previous_hash = previous_hash
              self.hash = hash(str(index) + data + str(previous_hash))
      return Block(0, "Genesis Block", "0")