added unit tests for recurrence modes
added unit tests for recurrence modes

stefan-balke/librosa,stefan-balke/librosa,carlthome/librosa,craffel/librosa,r9y9/librosa,r9y9/librosa,craffel/librosa,Cortexelus/librosa,Cortexelus/librosa,carlthome/librosa,stefan-balke/librosa,ruohoruotsi/librosa,r9y9/librosa,craffel/librosa,ruohoruotsi/librosa,ruohoruotsi/librosa,Cortexelus/librosa,carlthome/librosa