Write a more extensive vignette

[Jean-Baptiste-Camps]

We should write a more extensive vignette, taking elements from the documentation of the various functions, in a form that could be an alpha version of the paper presenting the package.

[Jean-Baptiste-Camps]

I have extended it a bit, but, for now, it is very close to what is available in help(stemmatology-package).

We should draw from the various papers/posters, and write a more extensive vignette, that could be the starting point of a JSS paper or equivalent, for instance.