Integrate compilation of assets (stylesheets, scripts, …) into ortfo/mk

[gwennlbh]

Right now, Stylus compilation and LiveScript compilation are done separately from ortfomk (see ewen-lbh/portfolio).
This should all be integrated with ortfomk (and will be possible with a more fleshed out CLI).
The following languages should be supported:

• Stylus
• SASS/SCSS (has a kinda-native Go compiler though LibSass!)
• CoffeeScript
• LiveScript
• TypeScript

Allow other to run by specifying them as build steps