PARQUET-93: Add support for protobuf to parquet-cascading

The parquet-cascading module currently includes code that lets Cascading write and read Thrift-based data to Parquet files. Protobufs is another popular alternative to Thrift which can be explicitly supported by leveraging the existing code in parquet-protobuf.
Not sure what you mean.  Was mostly just trying to duplicate the thrift definition that they used to test ParquetTBaseScheme.  Most of the test types in parquet-protobuf seemed like overkill for this new functionality.