New Engine : Mortevielle

Finally here's the pull request for the Mortevielle engine I mentioned in a blog post a while ago. The engine is the result of dreammaster and I joined efforts based on original sources provided by dotemu and Lankhor. the English translation has been done by one of our users, Hugo L.

In summary:
- Only the French DOS version is supported at this point
- The game is completable, tested under Windows 7. I did not test it on a BE system, and the last test under Linux isn't recent.
- A run with Valgrind would be great, I'd be thankful if someone did that.
- The game is missing sound. As a matter of fact, it's so terrible in the original that silence is a solace
- It doesn't impact common code, and in-tree coding should be, in a first step at least, essentially polishing. Adding support to Amiga and or Atari version would be great, in the future, but will also require a solution to handle speech, as it was delegating the speech synthesis to the OS.

I'm looking forward to your comments and (hopefully) your positive reactions!