Added hint about using as.numeric for arithmetic challenge in novice R lesson 06.
Removed erroneous cat statement from check.R in novice R lesson 06.
Removed exercise in novice R lesson 06 to detect absence of flag since too advanced.
Replaced loop with length in count-stdin.R for novice R lesson 06.
Added answer to line-count.R in novice R lesson 06.
Simplified exercise on adding usage message and also added solution in novice R lesson 06.