Fix typo of the word "assign" in comments

Erica,

I have enjoyed reading the 2nd edition of your excellent book this holiday season.  I am now integrating your code into my project.  While touring the code I noticed a recurring typo in comment blocks of the word "assign" (appears as "assing").

My fork is nothing more then the correction to this typo in comments.

I humbly submit this fix to you.  Thanks!

John
jlindwall@yahoo.com