[Bug Fix] Fix typo in SpatialSeparableConvoluiton layer name and add related docs (#2420)
[Bug Fix] Fix typo in SpatialSeparableConvoluiton layer name and add related docs (#2420)

* fix typo in spatialseparableconvoluiton name and add docs

* meet code review

* meet code review and fix tests

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