The 47-year-old musician and composer Mahmoud Turkmani was a highly accomplished oud player as a boy. As a young man, he rebelled against his upbringing and became a Communist. He left Beirut during the civil war and studied classical guitar at the Moscow Conservatory. From his adoptive home in Switzerland, he now enriches both Western and Eastern music with unorthodox works that fuse traditional and experimental elements and defy all categorization. Stefan Franzen met the artist