The class generated by Hadoop Record rcc should provide a static method to return the DDL string

The method will look like:

public static string getDDL();

With this class, when a map/reduce job write out sequence file swith such a generated class as its value class, the job
can also save the DDL of the class into a file.

With such a file around, we can implement a record reader that can generate the required class on demand, thus, can read
a sequence file of Hadoop Records without having the class a priori.