message: Doc for "pers" file format
diff: </table>
  \section Toolbox Toolbox
  + \subsection FileFormats File Formats
  + \subsubsection FileFormatsPers Persistence Diagram
  +
  + Such a file, whose extension is usually `.pers`, contains a list of persistence intervals.<br>
  + Lines starting with `#` are ignored (comments).<br>
  + Other lines might contain 2, 3 or 4 values (the number of values on each line must be the same for all lines):
  + \code{.unparsed}
  + [[field] dimension] birth death
  + \endcode
  +
  + Here is a simple sample file:
  + \code{.unparsed}
  + # Beautiful persistence diagram
  + 2 2.7 3.7
  + 2 9.6 14.
  + 3 34.2 34.974
  + 4 3. inf
  + \endcode
  +
  + Other sample files can be found in the `data/persistence_diagram`.
  +
  \subsection BottleneckDistanceToolbox Bottleneck distance
  \image html "perturb_pd.png" "Bottleneck distance is the length of the longest edge"
  <table border="0">
  