Change Title fo article

Remove the v letter from the "towvards" letter
Change the expoent of Xip
Merge pull request #55 from leard/master

Update RMDs 01_04 and 02_01
Fix coding for dates
Evaluate date/time code
updates/modifications to yhat example
Zip file of data used in lecture
Update PDF/PNG slides
Rename pdf slides
Some new PDFs
Merge remote-tracking branch 'github/master'

* github/master:
  Rename pdf slides
  Update PDF/PNG slides
  Zip file of data used in lecture
  updates/modifications to yhat example
  Evaluate date/time code
  Fix coding for dates