fix: multiple markdown tokens regexp

[halaaro]

Summary

Fixes issue for bold and italic text in headers as well as multiple sets of tokens

# `keyword1` and `keyword2`
# ***bold and italic***
# **bold** and *italic*

Currently, only the one set of tokens is removed from the table of contents and sidebar links:

Change makes the regexp non-greedy for matching the token pairs (*?) and matches up to 3 pairs of asterisks (\*{1,3}).

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
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N/A

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• Yes
• No

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Other information:

[halaaro]

@ulivz not sure how to proceed as this is my first PR, but please review this fix when you get a chance

[ulivz]

Thanks