Fix KLDCriterion forward (#2078)
Fix KLDCriterion forward (#2078)

* fix KLDCriterion

* add python doc

* add unit tests

* add api doc

yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL