This week Carole King, Diane Warren, and the Magnetic Fields' Stephin Merritt — all of whom appear on the _New York Times_ ' hotly-debated new list of the 30 Greatest Living American Songwriters — each wrote five-by-five mini puzzles for the publication's digital crossword section. Jeff Tweedy, despite admirably voting for himself, did not make the list. He did, however, get to write a full-sized…