Expose a method to get a project's contributors array

The function cvs_get_project_contributors_list directly outputs an HTML table, so it's useless if someone needs to display the commiters list in another way.
That would be interesting to have a function that only returns a contributors array.
The patch attached tries to limit this enhancement footprint, but it would be better to rename some of these functions, and maybe define a new theme_contributors_list function.