Support HDFS as a C++ plug-in module

Continuing from: https://github.com/hortonworks/orc/issues/149

There are C/C++ modules for reading from and writing to HDFS. There (may be) additional use cases for HTTP-based protocols like WebHDFS and S3.

As omalley states: "The C++ API has a pluggable interface for where to get the bytes. It already has a binding the local file system and it would be easy to extend it to other file systems or object stores.".

It would be nice to see a build of C++ ORC which includes HDFS support, as a build flag or otherwise provided as a module/separate repository.

I'd also like to see WebHDFS/S3 supported, once that baseline has been met.