Update some presentations and added new ones.
Fixed some errors and added new notes.
New lecture notes

Added some notes about normalization, probe summary, and started some
on Bioconductor.
Create HW1.md
Updated lecture notes
Minor update to question 2.
Added link to new slides
Improve the styling a bit.
trying to make a change and pull request
Changed the due date.
Create HW2.md

Second homework.
New lecture notes on differential_expression
Changes/additions to Bioconductor_intro.Rpres

I added some notes as well as a few changes that I needed to make in
order to get the presentation to work.
Updated presentations