Allowed more descriptive module names.
Note they must not have spaces in them; use underscores instead.
Each module (subdirectory in a Course) must have only one .csv file withe the  name "lesson.csv"
Removing renamed files.
module to lesson in content only
changed the rest of the instances of 'module' to 'lesson' in code and directory names
changed a few more instances of module to lesson in file names
a few tweaks so that R CMD check passes
fixed issue with showing pretty lesson names in lesson menu
Merge pull request #75 from ncarchedi/modnames

Changed all instances of 'module' to 'lesson' in code, comments, directories, and file names