Option to preserve HTML comments

[EvitanRelta]

Basic idea

Given these HTML:

<!-- BELOW IS A HEADING -->
<h1>Heading</h1>

<!-- BELOW IS A PARAGRAPH -->
<p>Paragraph</p>

<h1>Heading</h1>
<!-- ABOVE IS A HEADING -->

<p>Paragraph</p>
<!-- ABOVE IS A PARAGRAPH -->

<h1>Heading</h1>

<!-- INBETWEEN -->

<p>Paragraph</p>

The conversion will attempt to place the comment close to it's original siblings, like:

<!-- THIS IS A HEADING -->
# Heading

<!-- THIS IS A PARAGRAPH -->
Paragraph

# Heading
<!-- ABOVE IS A HEADING -->

Paragraph
<!-- ABOVE IS A PARAGRAPH -->

# Heading

<!-- INBETWEEN -->

Paragraph

No blank-lines on both sides

If the comment in the HTML has no blank-lines between it and BOTH its sibling elements, like:

<h1>Heading</h1>
<!-- NO BLANK LINES ON BOTH SIDES -->
<p>Paragraph</p>

then a blank-line will be added on both sides:

# Heading

<!-- NO BLANK LINES ON BOTH SIDES -->

Paragraph

Multiple blank-lines

In cases where theres more than 1 blank-line between the comment and its sibling elements:

<h1>Heading</h1>



<!-- 3 BLANKS ABOVE, 2 BLANKS BELOW -->


<p>Paragraph</p>

Then the blank-lines are preserved:

# Heading



<!-- 3 BLANKS ABOVE, 2 BLANKS BELOW -->


Paragraph

Comments inside elements

Heading

<h1>
  <!-- COMMENT BEFORE -->
  Heading
  <!-- COMMENT AFTER -->
</h1>

# <!-- COMMENT BEFORE -->Heading<!-- COMMENT AFTER -->

Paragraph

<p>
  <!-- COMMENT BEFORE -->
  Paragraph
  <!-- COMMENT AFTER -->
</p>

<!-- COMMENT BEFORE -->
Paragraph
<!-- COMMENT AFTER -->

List

<ul>
  <!-- OUTSIDE LIST-ITEM (BEFORE) -->
  <li>Item 1</li>
  <li>
    <!-- INSIDE LIST ITEM (BEFORE) -->
    Item 2
    <!-- INSIDE LIST ITEM (AFTER) -->
  </li>
  <li>Item 3</li>
  <!-- OUTSIDE LIST-ITEM (AFTER) -->
</ul>

<!-- OUTSIDE LIST-ITEM (BEFORE) -->
- Item 1
- <!-- INSIDE LIST ITEM (BEFORE) -->
  Item 2
  <!-- INSIDE LIST ITEM (AFTER) -->
- Item 3
<!-- OUTSIDE LIST-ITEM (AFTER) -->

Cases to add to issue's description:

• Heading
• Paragraph
• Tight-list
• Loose-list
• Blockquote
• Codeblock
• Table
• Hyperlink (ie. <a>)
• Text-formattings
  (ie. bold, italics, code, strikethrough, sub/superscript, underline)
• Comments inside tags
  (eg. <h1 <!-- COMMENT--> >)