Release v0.2.1

• Adding a changelog and bumping version in prep for release

• Updating CircleCI Badge

See also: https://github.com/ueberauth/guardian_paseto/blob/v0.2.1/CHANGELOG.md

v0.2.0 Paseto minor version bump

Bumping ex doc version

v0.1.0

Initial release containing callback implementation for the Guardian.Token behavior