Improve section 10.2.3.8 The $format System Query Option

Explicitly state that media types can be used in addition to the shorthand values atom, json, and xml. Explicitly state that parameters like odata.metadata=full can only be appended to the full media type like application/json. Remove last part of section stating that $format can be used in conjunction with $value: this doesn't make sense any more as $value uses the literal form defined in the ABNF, which is now also the literal form used by both Atom and JSON. Accepted: https://www.oasis-open.org/committees/download.php/48346/odata-meeting-26_on-20130221-minutes.html#odata-261