[enh] #181 move crc_pubkey.py to key package (BBC)

duniterpy/documents/__init__.py

duniterpy/documents/block.py

duniterpy/documents/block_uid.py

duniterpy/documents/certification.py

duniterpy/documents/identity.py

duniterpy/documents/membership.py

duniterpy/documents/peer.py

duniterpy/documents/transaction.py

duniterpy/documents/ws2p/heads.py

duniterpy/key/crc_pubkey.py

tests/documents/test_crc_pubkey.py