nh3

[jochenklar]

This PR adds the nh3 to clean markdown content. The feature can be controlled by settings.MARKDOWN_CLEAN = True | False and for more fine grained control:

MARKDOWN_CLEAN = True
MARKDOWN_CLEAN_KWARGS = {
    'attributes': {'*': {'style'}},
    'filter_style_properties': {'color'}
}

to allow, e.g., style arguments, but only the color property.

[jochenklar]

Things that will still work:

<a href="https://rdmorganiser.github.io">rdmo.org</a>

<strong>RDMO</strong>

<details>
  <summary>Epcot Center</summary>
  <p>
    Epcot is a theme park at Walt Disney World Resort featuring exciting attractions,
    international pavilions, award-winning fireworks and seasonal special events.
  </p>
</details>

Things that do not work anymore (without additional settings):

<a href="https://rdmorganiser.github.io" target="_blank">rdmo.org</a>

<span style="color: blue;">RDMO</span>

<span style="margin-right: 1rem;">RDMO</span>

<script>alert(1);</script>