Merge pull request #198 from asiviero/master

Added parameter to create playlists after downloading a class section
coursera: Remove superfluous comparison with True.
coursera: Remove trailing whitespace.
coursera: Wrap comment.
coursera: Avoid calling glob.glob too many times.
coursera: Use 4-space indenting.

I hope that I didn't modify the semantics of the code while doing so.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
coursera: Use `with` statement for writing a short file.

This way, we hope to be safer with respect to exceptions and doing it "The
Python Way" (TM).

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
coursera: Use fewer statements per line.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
coursera: Improve help message for the new option.

As suggested by me and agreed by John, we use "for".

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
Merging from coursera-dl/coursera