Fix typos in schema_org_rdfa.html

* oponent -> opponent
* occurreed -> occurred
* Add spaces to accidentally concatenated words
* Remove weird character after Boeing 747
* Add missing type names to Requirements docs

Signed-off-by: Dan Scott <dan@coffeecode.net>
Restore non-commercial Offer descriptions

Release 1.0f added non-commercial Offer descriptions (per
http://lists.w3.org/Archives/Public/public-vocabs/2014Feb/0028.html)
that accidentally regressed and were fixed in early April
(http://lists.w3.org/Archives/Public/public-vocabs/2014Apr/0093.html).

This fixes the most recent regression (hopefully forever!) :)

Signed-off-by: Dan Scott <dan@coffeecode.net>
Merge pull request #9 from dbs/non-commercial-offer

Restore non-commercial Offer descriptions
Merge pull request #7 from dbs/typos

Fix typos in schema_org_rdfa.html
Updating for v1.3 release.

Adding workPerformed property.
Preparing for v1.4 update, adding example for MusicEvent to go with
last week's v1.3 workPerformed addition.
removed a '.', used 'MusicGroup' instead of 'Organization'.
Added price and availability examples
Classical workPerformed example added to Event as well as to MusicEvent