Added Session04 and Session05 folders

Hello,

In session05 in my folder, I posted a program for the trigram homework. I created it without looking at the solution you posted (and forgot most of the details of what we reviewed in the previous class). Please, let me know what you think if you have time to look at it.
Thank you very much!
Michel.
looks good, but it is a bit slow once you get to a lot of characters to replace -- that's why the .translate() function is there. But this is great for now -- you can optimize it some day if you ever need to.