Merge pull request #5 from gr33ndata/master

Fixed a problem as it failed with non-ascii attributes
fixing unicode in python2.7
empty string should be treated as missing value
creat exception to properly raise the error to the end program
adding comments
Merge pull request #6 from flecox/master

fixing unicode for python2.7 and using exception for error merged

Thank you
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Contributors list updated
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Link to arff-datasets repository