Release v0.2.1

Release v0.3.0

Release v0.2.0

Rebrand (#17)

- Updated “Swiftype” references with “Elastic” in the readme and in the code.
- Renamed the published package to `elastic-enterprise-search`
- Changed versioning to be pre-release again, 0.1.0, since we are not yet in GA, just like we are doing for App Search.
- Updated copyright and license. Project is now Apache 2.0.
- Sending the analytics headers: X-Swiftype-Client and X-Swiftype-Client-Version
- Enabled CircleCI.