Refractory presentation

I cleared README.md in order it not to contain the manual. The README file is usually reserved to generic informations about authors, licence, and a synopsys of the interest of the package.

Then, I created a file called manual.md on the basis of your README.md file.
I wrote it using the markdown format (.md) because it is easy to read both in VIM or any text editor, and in more advanced text editors.

Could you please check that everything's right and merge if you agree with my changes?