Adding Eiffel language mode.

- Adding Eiffel highlight rules and Eiffel mode
- Use Sudoku grid example of Eiffel Rosetta Code project as Eiffel example
Add comment mark in Eiffel mode.
Remove eiffel example.

Current example is too large.
Adding the new Eiffel example.
Merge pull request #2055 from Conaclos/working

Eiffel programming language mode