docs: fix markdown parsing issue with underscores in link attributes and italic text

[codytubbs]

The python-markdown parser (via md_in_html extension) incorrectly handles underscores when a {:target="_blank"} attribute is combined with markdown italic text on the same line.

Current Behavior

In docs/why_this_guide.md, lines containing both link attributes and italic text are parsed incorrectly:

In [VU#425163]([https://kb.cert.org/vuls/id/425163){:target="_blank"}](https://kb.cert.org/vuls/id/425163)%7B:target=%22_blank%22%7D) _Machine learning classifiers ..._

Generates incorrect HTML:

<p>In <a href="[https://kb.cert.org/vuls/id/425163"><abbr](https://kb.cert.org/vuls/id/425163%22%3E%3Cabbr) title="CERT Vulnerability Note">VU#</abbr>425163</a>{:target="<em>blank"} _Machine learning classifiers trained via gradient descent are vulnerable to arbitrary misclassification attack</em>,

Root Cause

The md_in_html extension (enabled in mkdocs.yml) appears to misinterpret the underscore in _blank as a markdown italic marker when it appears before other italic text.

Solution

Escape the underscore in _blank when on the same line as italic text.

{:target="\_blank"}

Testing

Parsing comparison available at: https://babelmark.github.io/?text=In+%5BVU%23425163%5D(https%3A%2F%2Fkb.cert.org%2Fvuls%2Fid%2F425163)%7B%3Atarget%3D%22%5C_blank%22%7D+_Machine+learning_%2C%0A%0AIn+%5BVU%23425163%5D(https%3A%2F%2Fkb.cert.org%2Fvuls%2Fid%2F425163)%7B%3Atarget%3D%22_blank%22%7D+_Machine+learning_%2C
note: scroll down to section 2 to view results from python-markdown

Related Configuration

This issue involves the md_in_html extension listed under markdown_extensions in mkdocs.yml, which is likely related to the mkdocs-material* requirements.

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