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

Close #181 (closed).

duniterpy/documents/__init__.py

@@ -16,7 +16,6 @@
 from .block import Block
 from .block_uid import BlockUID, block_uid
 from .certification import Certification
-from .crc_pubkey import CRCPubkey
 from .document import Document, MalformedDocumentError
 from .identity import Identity
 from .membership import Membership