Added some slides on Bias

[Subbarao Kambhampati <rao@asu.edu>]

There seemed to be some questions in the class about "Bias" and what it 
means. I added a few slides right at the
beginning of the 5th october class (to the text classification slides of 
course).

Look at them. If you still have questions, I can spend some time discussing 
them next class

Rao