voided: updated example to match compaion doc

http://adlnet.gov/expapi/verbs/voided
Merge pull request #56 from bscSCORM/voided_url_fix

voided: updated example to match compaion doc
Merge pull request #58 from paul-esch/master

couple of small rewrites in 4.1.1, 4.1.7 and 4.1.8
rewrite of 4.1.6. Context

usual rewrite and restructuring.
Note that property 'platform' is not final yet in the original text.

Could not get the two code blocks to display properly using the
triple-apostrophe tags.