Preserve attributes as data attributes in html

Transforms:

```
<newline id="newline1" />
<newline id="newline1" count="2"/>
<para>hello</para>
<newline count="3" />
<para>lines</para>
<newline count="5" effect="underline" />

<para>newline with unsupported "effect" value</para>
<newline effect="x" />

<para>newline inside para</para>
<para>
<newline />
</para>
```

to:

```
<div class="newline" id="newline1"><br/></div>
<div class="newline" id="newline1" data-count="2"><br/><br/></div>
<p class="para">hello</p>
<div class="newline" data-count="3"><br/><br/><br/></div>
<p class="para">lines</p>
<div class="newline" data-count="5"
data-effect="underline"><hr/><hr/><hr/><hr/><hr/></div>

<p class="para">newline with unsupported "effect" value</p>
<div class="not-converted-yet">NOT_CONVERTED_YET: newline</div><newline
xmlns="http://cnx.rice.edu/cnxml" data-effect="x"/>

<p class="para">newline inside para</p>
<p class="para">
<div class="not-converted-yet">NOT_CONVERTED_YET:
newline</div><newline xmlns="http://cnx.rice.edu/cnxml"/>
</p>
```
Transform <space> in cnxml to html

Transforms:

```
<space id="space1" />
<space />
<space count="5" />
<space count="10" effect="underline" />

<space effect="x" />
```

To:

```
<pre class="space" id="space1"> </pre>
<pre class="space"> </pre>
<pre class="space">     </pre>
<pre class="space underline">          </pre>

<div class="not-converted-yet">NOT_CONVERTED_YET: space</div><space
xmlns="http://cnx.rice.edu/cnxml" data-effect="x"/>
```
Change <pre> to <span class="space"> and preserve attributes

Transforms:

```
<space id="space1" />
<space />
<space count="5" />
<space count="10" effect="underline" />

<space effect="x" />
```

to:

```
<span class="space" id="space1"> </span>
<span class="space"> </span>
<span class="space" data-count="5">     </span>
<span class="space" data-count="10" data-effect="underline">
</span>

<div class="not-converted-yet">NOT_CONVERTED_YET: space</div><space
xmlns="http://cnx.rice.edu/cnxml" data-effect="x"/>
```