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:
- All DOS versions are targeted by this engine.
- The French game is completable, tested under Windows 7, as well as its fan-made English translation. The German version needs a playthrough, and it wasn't tested it on a BE system.
- 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. Adding an optional text to speech module is an option.

I'm looking forward to your comments and (hopefully) your positive reactions!