Migrate "Ant" Guides to HTML5

[ptziegler]

This cleanup up the metadata and fixes broken links.
Contributes to
#3275

[ptziegler]

I'm not sure about the renaming part. As one can see in #3238, the validator is only applied on files with the .html file extension. And I don't see any option to make this configurable...

[akurtakov]

Renaming part is good to happen IMO but requires extra care as it may break links.

[ptziegler]

I've double-checked all references and I'm fairly certain to have gotten all links.

That said... 3s is suspiciously fast for the HTML check... Which makes me think that the script doesn't check anything...

[ptziegler]

@akurtakov If I understand the html5 workflow correctly, it's supposed to validate both .html and .htm files? If definitely ignores the .htm files, as there are still a lot that would fail the validation and I don't think it even cares about the .html ones...

[akurtakov]

@ptziegler Would you put errors on purpose in an .html and in .htm file so we can see what gets reported?

[ptziegler]

I did some tests and .html files still are validated, while .htm files are not. Though I still find the 3-4s to be quite low. Does it perhaps only check changed files?

[ptziegler]

i.e. this change is clearly invalid

[ptziegler]

Merging, as .htm files are only validated after #3342. I've reverted the change to the file extension, so this commit only contains the HTML cleanup again.