Use highlight library instead of highlight-regexp

Hi Juanjo,

This PR uses [highlight.el](http://www.emacswiki.org/emacs/?action=browse;oldid=HighLight;id=HighlightLibrary) library instead of `highlight-regexp`.
This allows to easily use `overlays` instead of `font-locking` which play nicer with `hl-line-mode` and `global-hl-line-mode`.

_Before_
![capture d ecran 2014-11-12 a 22 24 40](https://cloud.githubusercontent.com/assets/1243537/5022982/9a5e87e0-6abc-11e4-9255-36d0ade4c6d6.png)

_After_
![capture d ecran 2014-11-12 a 22 18 28](https://cloud.githubusercontent.com/assets/1243537/5022985/a26b5c56-6abc-11e4-9765-fd70ecff3683.png)

Cheers,
syl20bnr