* Validator now checks fixity block structure, additional fixity values in fixity block
* Validator now checks for repeated digests in manifest, fixity and state blocks (https://ocfl.io/1.0/spec/#E096, https://ocfl.io/1.0/spec/#E097, https://ocfl.io/1.0/spec/#E098)
* Move all the many README_*.md demos into docs folder
* Add build_demo_docs.sh to build demo descriptions in docs folder