Eiffel programming language mode

- Adding Eiffel highlight rules and Eiffel mode
- Use Sudoku grid example of Eiffel Rosetta Code project as Eiffel example
would be good to add 
```js
    this.lineCommentStart = "--";
    // this.blockComment = {start: "/*", end: "*/"}; if applicable
```

for togglecomment command

see https://github.com/ajaxorg/ace/blob/master/lib/ace/mode/javascript.js#L54-L55