Work-around Franklin bugs

[IanButterworth]

Fixes #2144

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[IanButterworth]

I'm fixing a few issues here, but it seems that the reason that the descriptions aren't being found is a bug in Franklin where it's supposed to, but no longer checking for a rss field, instead only rss_description
https://github.com/tlienart/Franklin.jl/blob/c06db25f51fa25e97db88c5b5d3a5dff657687e9/src/manager/write_page.jl#L221-L224

Also it seems that pagevar is an internal expects top level calls to have reset Franklin.PAGEVAR_DEPTH[] = 0 to guard against recursion. I don't believe that was the error here, but as noted before it was in another case, so I've set it to always be reset before a pagevar call. Seems adding a proper pagevar function to the API would be good?

fyi @tlienart

[IanButterworth]

I guess this was also not generating RSS feeds.. but I have no idea if that's a thing or how it works.

[IanButterworth]

I propose we merge this to fix the website, then investigate upstream Franklin fixes, then consider reverting unneeded parts of this once fixes are in.