Added extended Persona configuration
Added extended Persona configuration

ENV['PERSONA_AUDIENCE'] can now contain several audiences, and the
`authenticate` method may ask for a specific audience.
d2bit/timeoverflow,jordipujollarena/timeoverflow,d2bit/timeoverflow,jordipujollarena/timeoverflow,jordipujollarena/timeoverflow,coopdevs/timeoverflow,coopdevs/timeoverflow,d2bit/timeoverflow,d2bit/timeoverflow,coopdevs/timeoverflow,coopdevs/timeoverflow