To do that, I've reorganized the code

Test: with ocaml 4.08, it is impossible to load the same function twice.
Hence the need to define p.mli files for graphs with several nodes.

Also, track missing files and the alea-coloring exemples.

The rationale is that
 - it is not always the cmxs that is necessary .e.g., rdbg uses .cma or .ml
 - it makes more sense to refer to the source code