Dlhub-gateway

* [PR-315](https://github.com/jupyter/kernel_gateway/pull/315): Call tornado StaticFileHandler.get() as a coroutine

* [PR-314](https://github.com/jupyter/kernel_gateway/pull/314): Support serving kernelspec resources
* [PR-307](https://github.com/jupyter/kernel_gateway/pull/307): features.md: Fix a link typo
* [PR-304](https://github.com/jupyter/kernel_gateway/pull/304): Add ability for Kernel Gateway to ignore SIGHUP signal
* [PR-303](https://github.com/jupyter/kernel_gateway/pull/303): Fixed the link to section

* [PR-299](https://github.com/jupyter/kernel_gateway/pull/299): adds x_header configuration option for use behind proxies
* [PR-294](https://github.com/jupyter/kernel_gateway/pull/294): Allow access from remote hosts (Notebook 5.6)
* [PR-292](https://github.com/jupyter/kernel_gateway/pull/292): Update dependencies of Jupyter components
* [PR-290](https://github.com/jupyter/kernel_gateway/pull/290): Include LICENSE file in wheels
* [PR-285](https://github.com/jupyter/kernel_gateway/pull/285): Update Kernel Gateway test base class to be compatible with Tornado 5.0
* [PR-284](https://github.com/jupyter/kernel_gateway/pull/284): Add reason argument to set_status() so that custom messages flow back to client
* [PR-280](https://github.com/jupyter/kernel_gateway/pull/280): Add whitelist of environment variables to be inherited from gateway process by kernel
* [PR-275](https://github.com/jupyter/kernel_gateway/pull/275): Fix broken links to notebook-http mode page in docs
* [PR-272](https://github.com/jupyter/kernel_gateway/pull/272): Fix bug when getting kernel language in notebook-http mode
* [PR-271](https://github.com/jupyter/kernel_gateway/pull/271): Fix IPerl notebooks running in notebook-http mode

* [PR-266](https://github.com/jupyter/kernel_gateway/pull/266): Make KernelManager and KernelSpecManager configurable
* [PR-263](https://github.com/jupyter/kernel_gateway/pull/263): Correct JSONErrorsMixin for compatibility with notebook 5.2.0

* [PR-258](https://github.com/jupyter/kernel_gateway/pull/258): Remove auth token check for OPTIONS requests (CORS)

* Update compatibility to notebook>=5.0
* Remove kernel activity API in favor of the one in the notebook package
* Update project overview in the documentation
* Inherit the server `PATH` when launching a new kernel via POST request
with custom environment variables
* Fix kernel cleanup upon SIGTERM
* Fix security requirements in the swagger spec
* Fix configured headers for OPTIONS requests