Revert: Use simplified regex for html placeholders

[facelessuser]

Not sure how tests didn't get run on this, but it was completely
breaking all a lot of tests. This reverts the change.

Fixes #932

[facelessuser]

Spellchecker is finding lt in code blocks, that is why the spellchecker is failing. Not sure how you want us to handle this @waylan. Do I just add lt to the dictionary? Or can we exclude code tags?

[waylan]

Weird. I distantly recall checking that the tests passed on that because I expected them to fail. When the weren't failing, I accepted the change. But now, looking back, I don't see any indication that any tests even ran. Not sure what happened there. In any event we're getting 60 failing tests so this is the right move.

Also I just noticed that the note was added to the release notes for a previous release rather than a future release. Guess I wasn't paying close attention that day.

Spellchecker is finding lt in code blocks,

Code blocks are supposed to be skipped already. Not sure why that isn't happening.

[facelessuser]

@waylan #934 fixes it, it was finding the lt in the TOC.