Create osteoarthritis-and-cartilage-ama.csl

I have created a style for the Osteoarthritis and Cartilage journal. Although this style already exists in the CSL repo (http://www.zotero.org/styles/osteoarthritis-and-cartilage), it erroneously references the Vancouver superscript style (http://www.zotero.org/styles/vancouver-superscript). According to the O&C Guide for Authors, the style used should be American Medical Association (AMA) (http://www.zotero.org/styles/american-medical-association). I added 'ama' to the name of the style to distinguish the two.