EnsureDefaultListParams adds sort and per_page params to url.Values if they're not already there.

TODO: Change this to find tags? Tags can repeat.

GetFlagValue returns the parsed value of flagName.

GetTagValues parses tag values from the supplied string slice, which should be collected from the --tags flags.

GetUrlValues converts command-line args that look like name-value pairs into URL values.

InitRegistryRequest initializes a registry REST client and the params to be sent in a query string.

LoadProfile loads a BagIt profile.

LooksLikePreservationBucket returns true if the bucket name looks like the name of an APTrust preservation bucket.

NewRegistryClient returns a new client that can talk to the APTrust Registry.

NewS3Client returns a client that can talk to an S3 endpoint.

ParseArgPairs converts command-line args that look like key-value pairs into ArgPair objects.

PrettyPrintJSON converts unformatted JSON, such as that returned by the Registry, to formatted JSON.

ValidateManifestAlgorithms checks to see whether the user-specified manifest algorithms are allowed by the profile, and whether the user specified all of the profile's required algorithms.

ValidateTags verifies that tags required by the BagIt profile are present and contain valid values.

EXIT_BAG_INVALID is used primarily for apt_validate.

EXIT_NO_OP means the user requested help message or version info.

EXIT_OK means program completed successfully.

EXIT_REQUEST_ERROR means the remote server responded with a 4xx or 5xx HTTP status code.

EXIT_RUNTIME_ERR means program did not complete successfully due to an error.

EXIT_USER_ERR means the user did not supply some required option or argument, or the user supplied invalid options/arguments.