Added support for new Emacs major modes

Added support for `diff-mode` and `magit-mode` and improved support for `ido-mode`. These changes were applied in all Emacs theme variations.

Please take a look at the following images to see how the changes look like in `tomorrow-night`.

![diff-mode](https://f.cloud.github.com/assets/29534/110523/3f507786-6ac4-11e2-94ad-e79a5f347b4e.png)

![magit-mode](https://f.cloud.github.com/assets/29534/110526/50b6cf2a-6ac4-11e2-9b3d-a26a257f8ed7.png)

![ido-mode](https://f.cloud.github.com/assets/29534/110525/4d191c60-6ac4-11e2-823f-35397f37693d.png)