The Mets are hoping that veteran slugger J.D. Martinez can join the big league club to make his debut on Friday, manager Carlos Mendoza told reporters (including Anthony DiComo of MLB.com). In the meantime, DiComo adds that Martinez will move his rehab assignment up to Triple-A Syracuse while he works toward being ready to return to the big leagues. Martinez, 36, signed with the Mets on a one-year deal just before Opening Day. Thanks to the slugger missing the entirety of Spring Training, he beg