Add TextSet and update TextClassification examples (#684)
Add TextSet and update TextClassification examples (#684)

* add textset

* meet review

* update readme

* minor update

* minor

* minor

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