Add 18 with Erlang and improve with others

- Add 18 with Erlang
- Rewrite 18 with Scheme
- Improve 18 with Ruby and CoffeeScript
Add gitignore
Fix file permissions
Add 67 with Erlang and improve others

- Add 67 with Erlang
- Improve 67 with CoffeeScript
- Add required file for 67
Add 26 with Ruby (with rspec)