Converting blog back to jekyll from blosxom.

Modifications:
- background color
- added again the "previous" and "next" link
- math is now done with mathjax
- images are now properly placed.
- Syntax highlighting: instead of doing by hand, use pygments.
However, we cannot use multi-line so a cursor was added for long lines.
- updated some postes, especially the one about jekyll (missing the pygments section though)
- use a Makefile instead of a shell script to generate/upload.