* minor refactor circle event
* add coverage folder to gitignore
* remove old test environment
* removed obsolete grunt tasks
* remove obsolete node modules from package json
* formatting
* setup new test environment
* use karma, mocha, chai, sinon
* add needed modules to package json
* add karma configuration files for local dev tests and ci tests
* add first core test
* refactor core
* remove own Error construct, instead use new Error for better stack trace
* handle ‘song’ can be undefined in playSong
* do fail fast if an error occurs in playSong
* code formatting
* use new keyword for the database (new TAFFY()) constructor
* remove console.log statement
* update node modules
* update travis yaml file to use new grunt task for CI