Enable markdownlint no-inline-html

[silverwind]

With a few exceptions to accomodate current usage. Rule docs.

[silverwind]

Note that the rule is a bit too harsh in some cases, that's why the exception list is so long. For example to middle-align something, one can do:

<p align="center">
  I'm <b>bold</b>
</p>

In such a case, <b> usage is unavoidable and okay, but it would trigger the linter. So I'm unsure whether we should really enable it as it will give false-positives for all cases where one needs to use HTML attributes.

[silverwind]

I think I'll decide against this. It could be enabled of there is a smarter rule that detects HTML attribute usage, but as it is, the rule is just too crude to cover our use cases.