Switch to Emacs.
A Leanpub author shared this:
I just want to share a little fix I made to the markdown syntax in order to make it working with the code markup that this wonderful service requires when you want to insert a snippet of code in your books.
Just create a markdown.vim file in your .vim/after/syntax dir and add the following lines:
syn match markdownLeanCode '^<<(.*)$'
hi def link markdownLeanCode markdownH1
Now your code snippets won't mess up with the official markdown syntax provided by Vim