By Ayako Hirayama Daily Yomiuri Staff Writer Paul Martin's career as a Japanese sword specialist started in an unusual way. About 15 years ago, Martin was captivated by the beauty of Japanese swords he saw at the British Museum--not as a visitor, but as a security guard at the museum. "I saw Japanese swords close up for the first time. I didn't realize how beautiful they are," the 41-year-old B..