Add support to check if the release tarball checksum between different signed
assertions match.
This is only meant for quick verification, not for actual validation of the
assertion contents.
Keys are no longer imported automatically, use `--import-keys`
as an argument to import all public keys in the `gitian-pubkeys`
directory.
Keys are no longer refreshed automatically, use `--refresh-keys`
as an argument to refresh all public keys in the gpg keyring from
the sks server.
The verification step now uses the current working directory instead
of a hardcoded name in case the user renamed the gitian.sigs.
The verification now checks for the existance of each gitian.sigs
directory before running.
The user can specify custom monero and gitian-builder directory
locations. By default monero and gitian-builder are assumed on the same
level as the gitian.sigs repository.
