first pass on novice r reference sheet

addresses #663

First pass on the reference sheet.

almost just typed in any function/code I saw

Lots of work to do, but it's a start.
If we are using RStudio, I mention at the bottom of #615 that I click 'clear' and checking off 'include hidden objects'

if we should not use <code>rm(list = ls())</code> should we take this out of the lesson as well?