Kronos Quartet, with Sam Amidon, Olivia Chaney, Rhiannon Giddens, and Natalie Merchant Folk Songs Nonesuch CD   From its earliest recordings, which included transcriptions of jazz, Kronos Quartet has cast their net wide. The group’s repertoire encompasses music from the world over and from numerous composers in a variety of styles. To remind myself of Kronos’ earlier days, I put on their “Landmark Sessions” recordings of Thelonious Monk and Bill Evans. And what a reminder it was, pointing up the fluid nature of the quartet’s ability to shift tone and rhythmic feel to accommodate nearly whatever they approach.   On