SCSS + Variables + Relative Units

Alright. So this is the big one. 

The overall architecture of this theme has changed dramatically. I don't have a lot of time so had to do this in a few hours. Far from being perfect but I tried to keep it as simple as possible (for me, and everyone else). 

There is now a side nav (instead of the one on top). It looks like this:

![screen shot 2014-07-02 at 19 14 58](https://cloud.githubusercontent.com/assets/4347275/3454457/d996bb98-01d1-11e4-8ed8-4c7c3d59ae0a.png)

SCSS obviously allowed me to make variables. There is only 1 $main-color variable to change to make this theme unique. 

![screen shot 2014-07-02 at 19 17 30](https://cloud.githubusercontent.com/assets/4347275/3454493/4037ee30-01d2-11e4-85e2-8bc46bec297a.png)

![screen shot 2014-07-02 at 19 17 44](https://cloud.githubusercontent.com/assets/4347275/3454498/4f285178-01d2-11e4-912b-77b0a7df9b65.png)

Not ready for a merge right now but making this PR so the few persons interested in Hikari can try it out and help making this better. 

My plan is to move the bio description & social links (twitter, instagram etc) to _config.yml to make it even easier for people with little experience to get started with Jekyll. 

Cheers, 
Mathieu
No need for the `section` selector.