Adjusted sync/single arg passing + minor touches on the spec.
Merge pull request #541 from vasslitvinov/spec-w.r.t.-sync-variables

Adjusted sync/single arg passing + minor touches on the spec.

* Generic and blank-intent sync/single passing - by ref.
It used to specify readFE/readFF(), which I changed according to #420.

* Since the section opens with "normal reads and writes", I added "normal" in a couple of places where it talks about reads and writes.

* Refer to 'sync'/'single' as "type qualifiers" in a few places.

I did not see any other places in the spec that needed an update for #420, although I did not look too hard. The subsections on "Formal Arguments" and "Argument Intents" mention sync/singles only in the abstract-intent tables for blank and const. Those entries are correct IMO.