style the selected text/matched/unmatched brackets

The current style are not easily noticeable. The latest one colors was
picked from many dark theme like Sublime Monokai
![matching-brackets](https://cloud.githubusercontent.com/assets/281531/4500582/d85eebe4-4a95-11e4-9180-b33f55b5cacb.png)
![new-matching-brackets](https://cloud.githubusercontent.com/assets/281531/4500584/d85f3f72-4a95-11e4-8799-5f09709465db.png)
![new-select-text](https://cloud.githubusercontent.com/assets/281531/4500580/d85e8e42-4a95-11e4-89f4-6581eb5f0554.png)
![new-unmatched-brackets](https://cloud.githubusercontent.com/assets/281531/4500585/d861d2d2-4a95-11e4-95b9-822ea144d57b.png)
![select-text](https://cloud.githubusercontent.com/assets/281531/4500581/d85e98d8-4a95-11e4-9520-c78a226252a0.png)
![unmatched-brackets](https://cloud.githubusercontent.com/assets/281531/4500583/d85f316c-4a95-11e4-86dc-f0003d03970e.png)