text followed by image generates invalid ODF

[thorstenb]

With the example from #30 odpdown nests image draw frame inside span:

Welcome
====

Image is out of bounds ...
![image...](Testing_Pyramid.png)

yields

          <draw:text-box>
            <text:p>
              <text:span>
                <text:span>Image is out of bounds ...
</text:span>
                <draw:frame svg:width="12cm" svg:height="12cm" draw:z-index="0" draw:style-name="md2odp-ImageStyle" svg:x="7cm" svg:y="4cm" presentation:class="graphic" text:anchor-type="paragraph">
                  <draw:image xlink:href="Pictures/09298f92-d57d-49f6-9456-414aedad97b7.png" xlink:type="simple" xlink:show="embed" xlink:actuate="onLoad"/>
                  <svg:desc>image...</svg:desc>
                </draw:frame>
              </text:span>
            </text:p>
          </draw:text-box>

[thorstenb]

Hack-around currently:

Welcome
====

![image...](Testing_Pyramid.png)

Image is out of bounds ...