Added some regression lectures
started preprocessing lecture
first preprocessing lecture
Merge pull request #35 from jtleek/jeff

Jeff
pca lecture
Middle initial
Change author
More of Jeff's transcripts for EDA
Change author
Don't download data if it already exists
Skip stuff on graphics devices; covered in separate lecture
Images for expository graphs lecture
Promotion
Add reminder
Don't load data unless you have to
Change author; don't download data
Copy more images for exploratory plots
Clean up code a little
Merge two exploratory graphs lectures into one lecture
Rename old exploratory graphs lectures