Originally it was partially correct in that it did sound the bell, but it
also then exited the application and printed the details of the button --
the text didn't mention the latter aspect. This corrects that and removes
mention of the bell sound because we've now removed that.
* checkbox widget
* fixes
* Checkbox additions, fix content width in horizontal layout
* Update docs, add tests for checkbox
* Remove some test code
* Small renaming of test class
Co-authored-by: Will McGugan <willmcgugan@gmail.com>