Move most of hakyll-convert to Hakyll.Convert.Blogger.
hakyll-convert posts to markdown (content in HTML)

I can't really figure out how to work with Compilers, etc to do things
like extract tags.

We leave the content itself in HTML though, so it's really hakyll
metadata plus a big blob of HTML... the latter hopefully being
perfectly valid markdown
Kill unused Hakyll.Convert.Blogger bits.
We're just going to save output as .html with Hakyll metadata prefix
No need for intermediate format
Force UTF-8 on input and output and Unicode in between.
Seems to avoid encoding issues (hopefully not introducing any of my own)
Reformat dates in way Hakyll can understand.
Switch to published: instead of date:
Tidy up a little bit.
Friendlier output if post has no title.
More boring file stuff