A bare minimum service based on high-level server-side Akka HTTP API and Akka Actor.
Serves GET for:
GET /invitation HTTP/1.1
Host: 127.0.0.1:9000
and POST for:
POST /invitation HTTP/1.1
Host: 127.0.0.1:9000
Content-Type: application/json
{
"name": "name",
"email": "email@mail.com"
}