Multi-model-server

This release contains a minor bug fix for Python 2 support.
* Changed the python protocol handler between frontend and backend to support python 2 better.

* Load model API takes in JSON requests. 818
* Implementation of Ping API using the plugins SDK. 814
* Newer endpoint for predictions. `POST /models/{model-id}/invoke`. 823
* Handling OOM errors. MMS returns a HTTP 507 error code when there is a OOM error during runtime of MMS. 822
* Added changes to allow MMS have the same Management and Inference addresses 826
* Changes to MMS default behavior. MMS by default runs `POST /models` in a synchronous way and if there are `default_workers_per_model`, this value will be used when loading models. 836
* MMS configuration values can take environment variables. 841

This release contains multiple model server changes

Major features
1. Plugins support
1. SDK for plugins
1. Reference plugins implementation
1. MMS changes to support plugins
1. Feature to support default service file configured.
1. Feature to support return of custom HTTP headers from the model.

Minor features
1. Option to run MMS in the foreground
....
And multiple bug fixes

This release contains multiple model-archiver features and bug fixes.

Features
1. Added support for "no-archive"
2. Added feature to support optional conversion of ONNX model to MXNet model
3. Added integration test framework for model-archiver.

Features and Bug Fixes
* Published base MMS containers for Python 2.7 and Python 3.6 with Ubuntu 16.04 and nvidia/cuda 9.2 with CUDNN 7 on ubuntu 16.04.
* model-archiver changes to handle multiple archive formats
* model-server configurable through environment variables
* Contains multiple bug fixes

In this release we have addressed all the reported bugs and also added enhancements such as

Features and Major Bug Fixes
* Frontend listening on Unix Domain Socket.
* Support Asynchronous logging.
* Added documentation for batching support.
* Added features to support
* Starting default number of workers for models that are launched at MMS Startup time.
* Configurable response time out for individual models. This is the amount of time MMS waits for the model to respond to a request.
* Configure Maximum allowable request and response sizes.
* Changes for new Container images.
* Passing all HTTP headers to the backend worker.
* Adding shufflenet to the model server model-zoo.
* Adding example to bring sockeye model onto MMS.
... And bug fixes