Made change to trio vignette.

Here I made a small change in the title.

Note that earlier I had to remove all str() commands in the Sweave file.  These resulted in a $ being printed, which cause trouble when typsetting with LaTeX.  I'm not sure why it worked originally.

What I would like to do is start by editing Section 2 to include the FamilyExperiment class.  The data management methods, e.g., ped2trio, methods should be ported over to trioClasses, so that it contains all data related methods.  I can't decide if it is a good idea to move analytical functions from trio to trioClasses, but I do think data management methods should be moved to trioClasses.