Switch from compiler to optimizer

This way we don't have to think about what preprocessors might have been
used before autoprefixer.
Merge branch 'master' into optimizer

Conflicts:
	readme.md
	src/index.coffee
Merge branch 'master' into optimizer

Conflicts:
	src/index.coffee
Update docs links
Merge branch 'optimizer'
Add changelog
Mention that 1.8.x works with brunch 1.7.14+
Release v1.8.0