Prepare for archiving (#36)

Merge pull request #28 from firebase/jw-3xx-support-warning

Added warning about 3.x.x support to top of README

Update README for 3.0.0 release

Merge pull request #21 from jeromegamez/3.0

Add missing sprintf variable

Cleanup tests

Update README

Add .php_cs.cache to .gitignore

Remove deprecated code and calls

Update PHP-JWT to version ^3.0

Remove target-dir to be compatible with autoload.psr-4

Merge pull request #19 from jeromegamez/composer-updates

Add support URL and branch alias

Update README and CHANGELOG for v2.1.0