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.
Same as above.