Release 0.31.0.
* New functionality
- `sq key subkey add` allows to create and add a new subkey to an
existing certificate.
- The functionality of `sq-keyring-linter` is now available as
`sq keyring lint`.
- The new subcommands `sq key revoke`, `sq key subkey revoke` and
`sq key userid revoke`, allow writing to a file using the
`--output` option.
* Notable changes
- The `--keyring` option is now global and can be specified anywhere
when calling `sq`.
* Deprecated functionality
- The `--expires` and `--expires-in` options used in various
subcommands are deprecated in favor of the unifying `--expiry`.
- `sq key generate --export FILE` is deprecated in favor of the more
generic `sq key generate --output FILE`.
- The `sq revoke certificate` command has been renamed to `sq key
revoke`.
- The `sq revoke subkey` command has been renamed to `sq key subkey
revoke`.
- The `sq revoke userid` command has been renamed to `sq key userid
revoke`.