update CHANGELOG, adding a release note
# Master
+- IntOrString is now object thus it can be int or string. #18 #359
- Adding stream package to support calls like exec. The old way of calling them is deprecated. See [Troubleshooting](README.md#why-execattach-calls-doesnt-work)).
- config.http_proxy_url is deprecated. use configuration.proxy instead.
- Configuration is not a singleton object anymore. Please use Configuraion.set_default to change default configuration.
