Highlight c/c++ fenced blocks
Highlight c/c++ fenced blocks

Refs atom/language-gfm#33

rugk/markdown-preview,grimmer0125/markdown-preview-kramdown,sctlee/markdown-preview,tkssharma/markdown-preview,makyo/markdown-preview,Galadirith/markdown-preview,ArnaudRinquin/markdown-preview,atom/markdown-preview