add keras docs and fix GaussianSampler (#1028)
add keras docs and fix GaussianSampler (#1028)

* add keras layer docs and fix GaussianSampler

* add keras layer doc and fix GaussianSampler

* Update convolutional.md

* Update pooling.md

* add convolutional.md and pooling.md

* Update PythonZooKeras.scala

* Update convolutional.md

* Update core.md

* Update pooling.md

* Update normalization.md

* Update convolutional.md

* Update convolutional.md

* Update PythonZooKeras.scala

* Update torch.py

* Update dropout.md

* Update dropout.md

* Update PythonZooKeras.scala

* fix inputShape description of Merge

* Update dropout.md

* move torch.md to core.md and fix GaussianSampler

revise inputShape description and update examples of GaussianSampler

* Delete torch.md

* fix example data format

* #MultiShape changes to #Shape

* delete 'new set of' in Layers section

* #MultiShape changes to #Shape in Merge

* update overview description of GaussianSampler

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