removed backticks from first lesson of rprog
removed backticks from lesson 2 of rprog
removed backticks from lesson 3 of rprog
removed backticks from lesson 4 of rprog
removed backticks from lesson 5 of rprog
removed backticks from lesson 6 of rprog
small tweaks to new rprog lessons
more tweaks to rprog formatting etc
a few more small tweaks to rprog content