Schema version is now an optional argument rather than a required
argument. If schema version is not provided, look for a version
property in the data file. If found, try to use it as if it were the
argument value. If not found, log an error and exit. If schema version
is provided, still look for a version property in the data file. If it
does not match the provided version, log a warning. The provided version
is always used when available.

In cases where the version is the last property in the file, a backwards
search can get the version quickly. Set a three-second time limit for the
searches. If the time limit is reached, consider the version to be unknown.