0.4.0 DataAPI client & Unit tests

What's Changed

• tests: Added unit tests for Call API by @pashamesh in #6
• CI: added php_cs_fixer by @pashamesh in #7
• fix: Access token expiration timestamp is int by @pashamesh in #8
• feat: Replace RestAPI client by DataAPI client by @pashamesh in #9

Full Changelog: 0.3.0...0.4.0