Added workaround for problem setting invisibility

Added code to translate n or no into 0 for the -v flag to
create-course. This is a bit if a hack, but, it means v -1, which is
shown in examples in the doc, and hence probably in a lot of people's
code will continue to work exactly as-is.
Merge pull request #51 from bbusschots-nuim/140618_fix_course_create_visible_flag

Added workaround for problem setting invisibility