Specification clean-up

[eernstg]

This CL does not change the contents of the specification. It changes the following formatting properties:

• Lines with normal text (not \code{} and not math stuff) >80 chars are split to fit in 80 columns.
• \code{} and math elements not at the beginning of a paragraph that are large enough to need their own line are now consistently without indentation (\noindent).
• A number of unnecessary {} after LaTeX commands have been removed.
• One reference (\ref{...}) was undefined. A relevant reference occurred 3 lines earlier, so this undefined one was deleted.
• The wording in 2-3 comments was changed slightly to fit in 80 columns (only comments!).

We have preferred this kind of formatting for a long time, but generally changed long lines as part of other changes. It's a cleaner approach to fix all the long lines and inconsistent indentations in a single PR which is known to do just that, hence this PR.

[eernstg]

Thanks! Corrected a bunch of inconsistent quoted phrases (using <backquote>phrase<single_quote> rather than <single_quote>phrase<single_quote>, but keeping code in comments in the <backquote>usual(md.notation)<back_quote>).