[Issue] Pretty Printing

<mark> is a new HTML5 element used for highlighting:

https://developer.mozilla.org/en-US/...L/Element/mark
https://www.w3.org/TR/html5/textleve...e-mark-element

<mark> is mostly used in-line. For example:



After Pretty Printing in Sigil, each <mark> gets extra whitespace + placed on their own lines:



In many cases, this extra whitespace can completely botch the spacing (especially around punctuation).

The actual display before Pretty Print:

After Pretty Print:

For Pretty Printing, <mark> should probably be treated just like a <b> or <i> tag.