Pointer Capture is normative. Fix #269

[plehegar]

This section was incorrectly marked informative. Fixes #269

[patrickhlauke]

digging way back into a9bbc3c it seems originally the introduction to that section and the figure were informative.

<h1><dfn>Pointer Capture</dfn></h1>	
    <div class="informative">	
        <p>Pointer capture allows ...</p>	
        <figure id="figure_slider">	
            ...
        </figure>	
    </div>	
    	
    <section>	
        <h2>Setting Pointer Capture</h2>
        ....

Wonder if we should go for something similar again, or if we're ok just removing it and going with what you propose here.

[patrickhlauke]

Thinking about this some more (and looking at similar sections), it's probably fine to go with your proposed change here. There doesn't seem to be any harm in having the intro and examples there not explicitly marked non-normative... @NavidZ @mbrubeck et al, shout if you disagree.

[plehegar]

I added a commit to make the intro to that section informative. It requires a dedicated section but makes it clear.

[NavidZ]

Looks good to me.