Addresses https://github.com/adlnet/xAPI-Spec/issues/333

Also standardises , instead of - to list what's returned.
fixes https://github.com/adlnet/xAPI-Spec/issues/362

It seemed to make sense to bundle this in with other edits in the same area. 

Do we also need to look at section 6.3?
Merge pull request #372 from garemoko/return-values-as-code-blocks-in-section-7

return values as code blocks in section 7