[Improvement] Use glob pattern to search .txt and .lab files in train and test directory

[apsdehal]

It would be good if the searching for .txt and .lab in train directory used glob patterns like ./**/*.txt. This would allow structuring files inside the train directory for the user as he wants. I can work on this if you want this improvement included.

[jstypka]

Yeah, I think it would be cool. I think Python has a glob module that we could use for that, hopefully it should work for both Python 2 and 3.

[apsdehal]

Sure, I will start working on this within two weeks.