New "site-reveal" theme

This new theme is based in **reveal.js** library... 
With its, you will have a slideshow-based index and all the other pages rendered with the same structure and styling.

You have the possibility to choose 'sub themes' (each one with a different style).
But not only you can do it, because despite of your choice, the visitor of your webpage can easily apply another subtheme to your site just adding to the URI ?theme=his/her_choice.
You can also set different transitions between the slides in the index (and again the visitor can applied another transition).

In your conf.py file you will find two new attributes to easily choose your theme and transition:

```
# If you use 'site-reveal' theme you can select several subthemes
# THEME_REVEAL_CONGIF_SUBTHEME = 'sky' # You can also use: beige/serif/simple/night/default 

# Again, if you use 'site-reveal' theme you can select several transitions between the slides
# THEME_REVEAL_CONGIF_TRANSITION = 'cube' # You can also use: page/concave/linear/none/default
```
I hope you enjoy it, and as always... feedback welcome...

Abrazo.

Damián.