Added DM (Dream Maker) language.

Added:

 * DM (Dream Maker) language.
 * Sample DM file.

The DM language is used in an engine known as BYOND which allows users to easily create their own games in a language that is designed to be accessible for newcomers. I do not know how much a language has to be used on the site to be considered but searching for "BYOND" does show a lot of people using the language. I am also still learning git so if I have missed something then please let me know.