Anyone who gravitated towards Gary Clark Jr.’s, 2011’s “Bright Lights” EP, heard both the evolution of rock and roll and a savior of blues. The following year’s full-length debut, “Blak And Blu,” illuminated Clark’s vast musical spectrum. 2014’s “Gary Clark Jr.–Live” projected him into 3D — songs soared and drifted from psychedelic-blues to anthemic hip-hop, and all the way down to deep, dark, muddy blues. Now he has spread his musical wings even wider. “The Story of Sonny Boy Slim” accomplishes what his previous albums haven’t, spotlighting Gary Clark Jr., the artist first, — as producer, singer-songwriter — and string master second.