Add Lwan tests.

This patch adds Lwan web server alongside a benchmark that implements
all but one (database updates) tests.
fascinating. All the other databases have network overhead, it will be great to see how sqlite plays out. 

Without seeing the LWAN code here I can't verify if you are or are not caching - are you positive you are re-querying the database with each new request? 

How are you populating the database? If lwan DB tests do very well, I guess we will see an influx of other tests using SQLite too, so it would be good to have a standard way of populating. Any thoughts you have on this are welcome