Sagemaker

* doc-fix: Remove incorrect parameter for EI TFS Python README
* feature: ``Predictor``: delete SageMaker model
* feature: ``PipelineModel``: delete SageMaker model
* bug-fix: Estimator.attach works with training jobs without hyperparameters
* doc-fix: remove duplicate content from mxnet/README.rst
* doc-fix: move overview content in main README into sphynx project
* bug-fix: pass accelerator_type in ``deploy`` for REST API TFS ``Model``
* doc-fix: move content from tf/README.rst into sphynx project
* doc-fix: move content from sklearn/README.rst into sphynx project
* doc-fix: Improve new developer experience in README
* feature: Add support for Coach 0.11.1 for Tensorflow

* doc-fix: fix README for PyPI

* doc-fix: update information about saving models in the MXNet README
* doc-fix: change ReadTheDocs links from latest to stable
* doc-fix: add ``transform_fn`` information and fix ``input_fn`` signature in the MXNet README
* feature: add support for ``Predictor`` to delete endpoint configuration by default when calling ``delete_endpoint()``
* feature: add support for ``Model`` to delete SageMaker model
* feature: add support for ``Transformer`` to delete SageMaker model
* bug-fix: fix default account for SKLearnModel

* enhancement: Include SageMaker Notebook Instance version number in boto3 user agent, if available.
* feature: Support for updating existing endpoint

* enhancement: Add ``tuner`` to imports in ``sagemaker/__init__.py``

* bug-fix: Handle StopIteration in CloudWatch Logs retrieval
* feature: Update EI TensorFlow latest version to 1.12
* feature: Support for Horovod