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* Many small bug fixes:
* unknown subset types added to columns
* silent=True is really silent
* correct treatment of duplicated columns
* illegal file names and no filtering of user input from GEO to create the file names
* platform was not imported but used
* fixed issues of python 2 and 3 compatibility
* Logging replaced stdout and stderr + ability to set verbosity and log file
* Return downloaded paths from download functions
* Updated documentation according to Google docstring style guide
* Tests update
* Code refactored to be more PEP-8 friendly