Intra-word emphasis can match the wrong asterisks

[rriegs]

Describe the bug
Asterisks may be used to indicate intra-word emphasis, as in levio*SAH* for levio<em>SAH</em>, however, matching over-aggressively seeks to pair opening asterisks with asterisks at ends of words, sometimes skipping the intended intra-word asterisk.

To Reproduce
See this Marked demo link:

It’s levi*OH*sa, not levio*SAH.*

yields

It’s levi<em>OH<em>sa, not levio</em>SAH.</em>

Note the intra-word asterisks are converted to another layer of emphasis, rather than interrupting emphasis as they should. Another expression of this same bug is this:

*Some*thing is wrong *here.*

which yields

<em>Some*thing is wrong *here</em>

leaving unconverted asterisks.

Expected behavior
Compare to these CommonMark Dingus links, which yield

It’s levi<em>OH</em>sa, not levio<em>SAH.</em>

and

<em>Some</em>thing is wrong <em>here</em>

[UziTech]

see #1522

There are currently 47 common mark spec tests in the Emphasis and strong emphasis category that are not passing.

If you would like to help PRs are always welcome. 😁