Increase perfomance by PostCSS 5.0

PostCSS 5.0 will have custom parsers/stringifier. So you can speed up tool by removing CSS generation and then PostCSS parsing. With custom parser you can “parse” JS object to PostCSS AST objects.

https://github.com/postcss/postcss/tree/valac#custom-syntaxes

PostCSS 5.0 is still in progress, so this is a long term issue. But we are really close to release (just docs and testing).