[README][xs]: stub description.
[layouts][xs]: add support for page bodyclass attribute.
[#8][m]: scrape readme info for github extensions and display it.
[ext][m]: add readmes to existing extensions.
[ext][xs]: remove demo geo extension entry (not real).
[#8,search][m]: basic filter now working again.

* Also refactor search code quite a bit.
[misc][s]: add links to download full extension list in footer.