cloned from https://github.com/dairiki/lektor-markdown-image-attrs
and cleaned up unneccessary files

add markdown-image-attrs 0.2.1 plugin

See merge request !73

Fix deprecation warnings in SCSS

See merge request !74

Disallowing /static means our images can't be indexed.
It also breaks twitter's metacards (see donate-static#97)

The robots.txt spec isn't as strict as I thought, so we don't need to worry
about whitespace or capitalization

Fix up robots.txt

See merge request !75