docs(manual): fix duplicate labels and correct section hierarchy

[tueda]

This PR fixes duplicated labels substaevaluate and funmatch. It also promotes Optimization options of the Format statement from a subsection to a section, because that part had no section heading, which resulted in a "hierarchy problem" (LaTeX2HTML generates 10.0.1).

There is still something weird in the LaTeX source. There are several instances of \setcounter{equation}{...}:

doc/manual/statements.tex
532:\setcounter{equation}{2}
4691:\setcounter{equation}{3}
5369:\setcounter{equation}{4}
5376:\setcounter{equation}{5}
5971:\setcounter{equation}{6}
6021:\setcounter{equation}{7}

Do we need these counter manipulations?

[coveralls]

coverage: 58.03% (-0.01%) from 58.04%
when pulling 1cd423f on tueda:pr/fix/manual-labels-and-sections
into 9b0d11c on form-dev:master.