midi vs. mid prefix

Seems like this isn't an issue at the SPARQL endpoint, but at least in the "latest" dump the prefixes are "mid" throughout, whereas the SPARQL documentation refers to "midi". Not a big deal, but might be good to make a note of this in the documentation. 

There are also a couple other discrepancies between the documentation and "latest", e.g. "mid:tick" as opposed to "midi:tickOffset". 