Add preliminary Lwan support

This patch series adds necessary support to run Sailor applications under [Lwan](http://lwan.ws). No applications beyond whatever `sailor_create` creates has been tested, so it's very likely to break under real use cases.

In fact, most of the Remy interfaces contains hardcoded values which will cause trouble; that's because interfaces to obtain these values are not available in Lwan yet. Changes to obtain live values will be provided as they're implemented in Lwan.