em config file

I think this is a good starting point to build off of and, for the most part, solves https://github.com/EventedMind/em/issues/6 
Refactoring this to a better scalable code:

```javascript
getRealExtensionFor: function(fileType) {
  var fileAlternatives = {
    'html': ['jade'],
    'css': ['stylus', 'less', 'scss'],
    'js': ['coffeescript', 'typescript']
  };

  // I'm supposing that realExtension always exists.
  return this.getAltResourceOrDefault(fileType, fileAlternatives[fileType]).realExtension;
}
```

You can do that to some other functions I've seen in this commit.

@scott-mcpherson if you feel uncomfy with my code review, please let me know.