Fix HTML_ATTR rendering (naive)

- was missing spaces between attributes when rendering to org
- was duplicating attributes when rendering to html - now we join / replace
  attributes depending on the name - for now only class & style are appended

org/testdata/misc.html

@@ -57,7 +57,8 @@ foo
 <a href="https://www.example.com"><em>this</em> <strong>is</strong> <span style="text-decoration: underline;">markup</span>!</a>
 </p>
 </blockquote>
-<h3><a href="https://github.com/chaseadamsio/goorgeous/issues/77">#77</a>: Recognize <code class="verbatim">code</code>--- as code plus dash</h3>
+<h3><a href="https://github.com/chaseadamsio/goorgeous/issues/72">#72</a>: Support for #+ATTR_HTML</h3>
+<img src="https://golang.org/doc/gopher/pkg.png" alt="Go is fine though." title="https://golang.org/doc/gopher/pkg.png" width="300" style="border:2px solid black;"/>
 <h3><a href="https://github.com/chaseadamsio/goorgeous/issues/75">#75</a>: Not parsing nested lists correctly</h3>
 <ul>
 <li>
@@ -73,6 +74,7 @@ sub bullet
 </ul>
 </li>
 </ul>
+<h3><a href="https://github.com/chaseadamsio/goorgeous/issues/77">#77</a>: Recognize <code class="verbatim">code</code>--- as code plus dash</h3>
 <h3><a href="https://github.com/chaseadamsio/goorgeous/issues/78">#78</a>: Emphasis at beginning of line</h3>
 <p>
 <em>italics</em>