Link toolbox help with Scilab one How to make hyperlink in toolbox help pointing to Scilab's items

## Description

Since Scilab 5.3.1, the hyperlinks in a toolbox help can be used to point on any help pages or to execute demos in the console.

Now you can link a demo Uicontrol demo or execute a script about.sce

## Details

- To link from two external modules, the syntax is: <link type="scilab" linkend="module_name.help/fun_in_module_name">fun_in_module_name</link> Usually, the name of the function is the id of the page.

- To link from a external module to a Scilab function, the syntax is: <link type="scilab" linkend="scilab.help/bvode">bvode</link> Usually, the name of the function is the id of the page.

- To enable the execution of a script, the syntax is: <link type="scilab" linkend="mytoolbox.exec/macros/fooexec.sce">macros/fooexec.sce</link>

- To enable the execution of a demo, the syntax is: <link type="scilab" linkend="mytoolbox.demos/mydemo.dem">My demo</link>

## Examples

    <?xml version="1.0" encoding="UTF-8"?>
        <refentry xmlns:scilab="http://www.scilab.org"
                  xmlns="http://docbook.org/ns/docbook"
                  xmlns:html="http://www.w3.org/1999/xhtml"
                  xmlns:db="http://docbook.org/ns/docbook">
          <refnamediv xml:id="foo">
            <refname>Foo</refname>
            <refpurpose>calculates foo</refpurpose>
          </refnamediv>
          <refsection>
            <!-- Link on Scilab's help -->
            <para>Firstly a link on <link type="scilab" linkend="scilab.help/bvode">bvode</link> in the Scilab Doc</para>
            <!-- Link on a demo, foodemo must be in toolbox_path/demos/ -->
            <para>Secondly a link on <link type="scilab" linkend="mytoolbox.demos/foodemo">My demo</link></para>
            <!-- the executed macro will be toolbox_path/macros/fooexec.sce -->
            <para>Thirdly a link on <link type="scilab" linkend="mytoolbox.exec/macros/fooexec.sce">macros/fooexec.sce</link></para>
            <!-- a link for erroneous links -->
            <para>Fourthly a link on <link type="scilab" linkend="scilab.help/invalidlink">invalid link</link></para>
          </refsection>

          <programlisting role="example">
            plot3d() // should link on plot3d
          </programlisting>
        </refentry>