Minor updates to comments of the previous repository_tool.py commit.
Update repository_tool-diagram.png to list disable_console_log_messages().
Rename disable_console_messages().
add_key() -> add_verification_key()
remove_key() -> remove_verification_key()
release.json -> snapshot.json
Update repository_tool-diagram.png
Update README following the renamed functions and release role changes.
Minor edits, such as removing lint left over from a previous merge conflict.
Add support for encrypted (and public ed25519 keys) TUF key files.
Add support for ed25519 keys, signatures, and key files in libtuf.py.
Update libtuf.py diagram.
Move canonical encoding operations to the create and verify key functions.
