Separated the API from the POC module and turned it into a library.

Full Changelog: v2.0.0...v2.0.0

Arrange supporting codes

• Fix snippets loading error on spring-rest-doc (manual)
• Remove all unnecessary dependencies
• Add test codes for refresh_token

v1.0.2

• Fix an important error on the exposed refresh token API, /api/v1/traditional-oauth/token

The first release

• All the information on the release is indicated on README.md, as this is a first release.