This is me mainly scratching an itch, but it is a small proof of
concept on how possible it is to embed a HTTP server into PostgreSQL
as a background worker.

Right now it uses libebb as an event-driven HTTP server. As the
background workers only have a single connection to the database, one
process can only serve one client at a time. Libebb support multiple
connection, you better not connect multiple times.

Other possible HTTP implementations:

 * https://github.com/valenok/mongoose.git - tried it, got complicated
   because it wanted to control forking.
 * https://github.com/joyent/http-parser - a plain HTTP parser, might
   be useful if I end up with a custom HTTP server.