Added support for use case in which user submits single training and tes...

...ting files via train_file and test_file in the configuration file.

This pull request addresses the following issue:

"Train/test requires feature files to have the same name but in different directories". #12

Let me know what you think about this solution--it's both hacky and elegant at the same time.  It's elegant in the sense that it is able to reuse all of the run_configuration() code as-is, with no modifications to the general architecture.  It's hacky in the sense that some of the pre-existing variables are being reused with new meanings for this new use case (e.g., train_path and test_path specify the full file paths of the input files instead of the directory paths).  The code passes nosetests and works for the use cases I envisioned, but new unit tests and documentation need to be added.  Please point me in the right direction for this if you'd like me to do it.
Done.  Thanks for pointing that out.