removed type checking in unit conversion (not needed)
Merge pull request #12 from stevejpurves/master

October tutorial code
case sensitive I think
Fix broken link to the PDF of Steve Purves

The dir name in the link needed to be capitalized. 
A link to the raw file makes it easier to download the PDF.
Merge pull request #13 from leouieda/patch-1

Fix broken link to the PDF of Steve Purves - cheers Leo!
Merge branch 'master' of https://github.com/seg/tutorials
adding Dec issue
added to README
new version
pre-pub changes
case
figure 2
adding reference
added link to tutorial online