Add Cram test syntax highlighting

[johnridesabike]

It looks like this was added to the VSCode extension a while ago, but not the Vim one. We could probably just port those highlight rules? ocamllabs/vscode-ocaml-platform#193

[Julow]

VSCode highlighting rules can't simply be ported to Vim but thankfully the syntax is simple.

I've been happily using the syntax file that comes with the Python cram project: https://github.com/myint/cram/blob/master/contrib/cram.vim
(to install it, copy it to ~/.vim/after/ftplugin/cram.vim and add this to your vimrc: autocmd BufNewFile,BufRead *.t setlocal ft=cram)
I wish this (GPL licensed) could be integrated to vim-ocaml (which doesn't state its license).

[johnridesabike]

Given that the vim-ocaml files are synced with Vim, I assume that they must be under the same license as Vim itself? I agree that this repository should explicitly state that. (But that's probably a separate issue.)

Back on topic: adding the Python cram project's syntax file to my ~/.vim seems to work great. I would definitely welcome having it integrated into vim-ocaml, if it's possible.