add changelog

Author: Zsailer

CHANGELOG.md

@@ -0,0 +1,48 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+
+## [0.2.0] - 2019-12-19
+
+### Added
+- `extension` submodule ([#48](https://github.com/jupyter/jupyter_server/pull/48))
+    - ExtensionApp - configurable JupyterApp-subclass for server extensions
+        - Most useful for Jupyter frontends, like Notebook, JupyterLab, nteract, voila etc.
+        - Launch with entrypoints
+        - Configure from file or CLI
+        - Add custom templates, static assets, handlers, etc.
+        - Static assets are served behind a `/static/<extension_name>` endpoint.
+        - Run server extensions in "standalone mode" ([#70](https://github.com/jupyter/jupyter_server/pull/70) and [#76](https://github.com/jupyter/jupyter_server/pull/76))
+    - ExtensionHandler - tornado handlers for extensions.
+        - Finds static assets at `/static/<extension_name>`
+
+### Changed
+- `jupyter serverextension <command>` entrypoint has been changed to `jupyter server extension <command>`.
+- `toggle_jupyter_server` and `validate_jupyter_server` function no longer take a Logger object as an argument.
+- Changed testing framework from nosetests to pytest ([#152](https://github.com/jupyter/jupyter_server/pull/152))
+    - Depend on pytest-tornasync extension for handling tornado/asyncio eventloop
+    - Depend on pytest-console-scripts for testing CLI entrypoints
+- Added Github actions as a testing framework along side Travis and Azure ([#146](https://github.com/jupyter/jupyter_server/pull/146))
+
+### Removed
+- Removed the option to update `root_dir` trait in FileContentsManager and MappingKernelManager in ServerApp ([#135](https://github.com/jupyter/jupyter_server/pull/135))
+
+### Fixed
+- Synced Jupyter Server with Notebook PRs in batches (ended on 2019-09-27)
+    - [Batch 1](https://github.com/jupyter/jupyter_server/pull/95)
+    - [Batch 2](https://github.com/jupyter/jupyter_server/pull/97)
+    - [Batch 3](https://github.com/jupyter/jupyter_server/pull/98)
+    - [Batch 4](https://github.com/jupyter/jupyter_server/pull/99)
+    - [Batch 5](https://github.com/jupyter/jupyter_server/pull/103)
+    - [Batch 6](https://github.com/jupyter/jupyter_server/pull/104)
+    - [Batch 7](https://github.com/jupyter/jupyter_server/pull/105)
+    - [Batch 8](https://github.com/jupyter/jupyter_server/pull/106)
+
+### Security
+- Added a "secure_write to function for cookie/token saves ([#77](https://github.com/jupyter/jupyter_server/pull/77))