Appearance of " Hilbert Sorting" in documentation.

[albert-github]

Looking at the documentation of the Spatial_sorting package (Spatial_sorting/index.html)

the gray background is a bit strange and comes from the fact that a <blockquote> is used (in Spatial_sorting/doc/Spatial_sorting/Spatial_sorting.txt).

Probably better would bee something like:

resulting from:

\section sechilbert_sorting Hilbert Sorting

In 2D, one can construct a space filling curve, that is a mapping \f$ f\f$ of \f$ [0,1]\f$
to the unit square \f$ [0,1]^2\f$, such that \f$ f(0)=(0,0)\f$ and \f$ f(1)=(1,0)\f$
in the following way:
the unit square is subdivided in four such that

\par
\f$ f([0,\frac{1}{4}])=[0,\frac{1}{2}]^2\f$,
\f$ f([\frac{1}{4},\frac{1}{2}])=[0,\frac{1}{2}]\times[\frac{1}{2},1]\f$,
\f$ f([\frac{1}{2},\frac{3}{4}])=[\frac{1}{2},1]^2\f$,
and
\f$ f([\frac{3}{4},1])=[\frac{1}{2},1]\times[0,\frac{1}{2}].\f$
<br>
\f$ f(\frac{1}{4})=(0,\frac{1}{2})\f$,
\f$ f(\frac{1}{2})=(\frac{1}{2},\frac{1}{2})\f$, and
\f$ f(\frac{3}{4})=(1,\frac{1}{2})\f$.

[albert-github]

I've just pushed a proposed patch, pull request #7705