Merge pull request #1 from sgagnon/master

Adding Tutorial 2 files and materials
Merge pull request #2 from sgagnon/master

Add some explanatory text to second tutorial
Merge pull request #3 from sgagnon/master

Add third R tutorial with supporting data
Merge pull request #4 from sgagnon/master

added some instructions for installing R, etc., + looking at the tutorial files
Adding .gitignore and removing cruft
Add chunk names to tutorial 2 and tweak formatting
Name and reformat tutorial 3
Remove figure pngs from the repo
Add figure/ dir to .gitignore
Merge pull request #5 from mwaskom/ignore_figures

Ignore figures generated during the .Rmd weaving process