PyMdown Extensions has ReDOS bug in Figure Capture extension

PyMdown Extensions is a set of extensions for the `Python-Markdown` markdown project. Versions prior to 10.16.1 have a ReDOS bug found within the figure caption extension (`pymdownx.blocks.caption`). In systems that take unchecked user content, this could cause long hanges when processing the data if a malicious payload was crafted. This issue is patched in Release 10.16.1. As a workaround, those who process unknown user content without timeouts or other safeguards in place to prevent really large, malicious content being aimed at systems may avoid the use of `pymdownx.blocks.caption` until they're able to upgrade.