Pass done on "Improving Debugger Context" and "Laser Beam Path"

First a question... was "Leaving Notes in Your Code" from the original tutorial left out on purpose?
http://squeak.preeminent.org/tut2007/html/035B.html

I've completed my review of Improving Our Debugging Context."  That was a nice addition on top of the original tutorial.  In an earlier chapter Stef had changed the original default grid size from 1x1 to 5x5. I didn't understand why then but 5x5 seemed too big, so I had changed it to 3x3.  I found out why in this chapter, and since my 3x3 change had already been integrated, I propagated this through this chapter. I think it ends up working just as well.   This was one commit.

I also completed my review and restructure of the Laser Beam Path chapter (it was in the same file but has its own commit.)    I've made some major changes to try to explain things better, so its probably better reviewed as a whole PDF rather than a `git diff`. 

I'll next proceed to take the lead with creating a new file and chapter for "Path Calculation"
http://squeak.preeminent.org/tut2007/html/041.html