Multiple sequential paragraphs that share the same exact properties should be merged

[kylegibson]

Otherwise we can end up with output like this:

  <p>
   <span style="margin-left:0.50em">
    <span class="pydocx-left">
     <span class="pydocx-underline">
      <strong>
       P
      </strong>
     </span>
     <span class="pydocx-underline">
      <strong>
       O
      </strong>
     </span>
     <span class="pydocx-underline">
      <strong>
       L
      </strong>
     </span>
     <span class="pydocx-underline">
      <strong>
       I
      </strong>
     </span>
     <span class="pydocx-underline">
      <strong>
       C
      </strong>
     </span>
     <span class="pydocx-underline">
      <strong>
       Y
      </strong>
     </span>
    </span>
   </span>
  </p>

[jhubert]

:+1: