FRAMINGHAM – A half century after setting a new standard for banjo playing, Eddie Adcock remains one of bluegrass’ most innovative artists. Joined by his wife, Martha, with ex-Country Gentlemen bandmate Tom Gray on bass, Adcock performs on Feb. 16, the first of the thirty-third annual Joe Val Bluegrass Festival’s three days at the Sheraton Hotel in Framingham. “Eddie’s unique musical wizardry is frequently mind-blowing . . .