add MeanAbsolutePercentageCriterion & MeanSquaredLogarithmicCriterion (#1916)
add MeanAbsolutePercentageCriterion & MeanSquaredLogarithmicCriterion (#1916)

* add MeanAbsolutePercentageCriterion & MeanSquaredLogarithmicCriterion

* add docs

* meet pr comments

* meet pr comments

* exchange keras input target

* update readme

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