Update bookmap proposal with amendments support

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE bookmap PUBLIC "-//OASIS//DTD DITA 2.0 BookMap//EN" "bookmap.dtd">
<bookmap>
    <booktitle>
        <mainbooktitle>Test</mainbooktitle>
    </booktitle>
    <ditavalref href=""/>
    <mapresources>
        <keydef keys="test" href=""></keydef>
    </mapresources>
</bookmap>