Updated to utilize php8

Updated to support php release 8 (#11)

* Adopted PSR-12
* Refactored to support latest phpunit
* Moved unittests
* Dropped old php version
* Implemented strict type checking
* Build on all platforms

Finally after more than 4 years in development. The first stable release.

Merge pull request #7 from localgod/build_cleanup

Build cleanup