Add changelog (#84)

* Add changelog

* Update per review

* update release date

CHANGELOG.md

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+# Changelog
+All notable changes to this project will be documented in this file.
+
+## 0.1.0 – 2017-08-28
+### Breaking changes
+- You need add two config parameter to `config.json`:
+  - `listen` defines the ip address and port Matterpoll will listen for requests. Default is `localhost:8505`
+  - `token` is the mattermost token. You should copy it from Integration > Slash Commands at your Mattermost server.
+- Removed `-p` option. Choosing the port is now done via `config.json`
+
+### Added
+- Polls are posted as a bot user
+- You can use single and double quotation instead of backticks
+- We now verify the Mattermost token to make sure requests are valid
+- The ip address Matterpoll should listen for request can now we configured via `config.json`
+- You can choose the config file via `-c` option
+- Go 1.7 to 1.9 are now supported
+
+### Changed
+- A lot of unittests were added
+- Moved from Mattermost APIv3 to APIv4
+
+### Fixed
+- Removed dependency of glide
+- Mattermost warning about empty message
+
+## 0.0.2 – 2017-04-19
+### Added
+- Ci builds via travis
+
+### Changed
+- Use 8505 as default port
+
+### Fixed
+- Fixed setup documentation
+
+## 0.0.1 – 2017-04-02
+- First Version