Merge branch 'master' into coursera
Merge remote-tracking branch 'swirldev/coursera' into coursera
DESCRIPTION and NAMESPACE fixed to pass devtools::check. They were probably corrupted in earlier, Byzantine sequence of merges and deletions.
removed excess comma in DESCRIPTION
dealt with merge conflict in DESCRIPTION
some much needed updates to docs using roxygen 4.0.0
dealt with case where 'lesson' file has no extension
removed test lesson from swirl -> swirl_courses repo
Documented answerTests2.R and roxygenized.
minor corrections to documentation
a couple small tweaks to output
fixed message and hardcoded course_name
add check for incorrect - i.e. empty result
fixed small bug in content
small tweak to coursera code
changed message received if too many skips
updated course menu blurb
Improved cheat resistance.