Use m:math/@alttext for MathML in bookmark

[ToshihikoMakita]

Use m:mathml/@alttext when making bookmark (or text mode processing) described below:

http://www.daisy.org/z3986/structure/SG-DAISY3/part2-math.html#L232

[ToshihikoMakita]

Implemented in development branch.

DITA authoring:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="cMathmltest">
    <title>MathML Test <equation-inline><mathml><m:math id="m01" alttext="y equals m x plus b" xmlns:m ="http://www.w3.org/1998/Math/MathML" display="inline">
        <m:mrow>
            <m:mi> y </m:mi>
            <m:mo> = </m:mo>
            <m:mrow>
                <m:mi> m </m:mi>
                <m:mo> &#x2062; <!--invisible times--> </m:mo>
                <m:mi> x </m:mi>
            </m:mrow>
            <m:mo> + </m:mo>
            <m:mi> b </m:mi>
        </m:mrow>
    </m:math></mathml></equation-inline></title>
    <shortdesc>The title contains <xmlelement>mathml</xmlelement> element.</shortdesc>
</concept>

The formatting result: