Added deprecate warning to CrossEntropy and removed it from test_sgd
merge
Merge remote-tracking branch 'upstream/master' into no_crossentropy_class
added deprecated warning to CrossEntropy
added import warnings
Merge remote-tracking branch 'upstream/master' into no_crossentropy_class
Merge pull request #545 from bouthilx/no_crossentropy_class

Get rid of CrossEntropy (#275)