Replace mappend with its infix version, (<>)
Simplify an expression
Add note on SASS support in README
Move README to README.md
Add an empty robots.txt
Add a rule to compile SCSS

Caveat: if styles/x.css and styles/x.scss both exist, they will both output to
_site/styles/main.css, overwritting each other.
Add proper SCSS and concatenation support

Now css and scss files with the same name can coexist. All the files
that are under src/styles are passed to sass and concatenated into one
final styles.css file.
Add .sass-cache/ to .gitignore