added search endpoint

* check whether one or more phone numbers are registered with
  the signal service.

see #50

src/main.go

@@ -49,6 +49,9 @@ import (
 // @tag.name Reactions
 // @tag.description React to messages.
 
+// @tag.name Search
+// @tag.description Search the Signal Service.
+
 // @host 127.0.0.1:8080
 // @BasePath /
 func main() {
@@ -204,6 +207,11 @@ func main() {
 			reactions.POST(":number", api.SendReaction)
 			reactions.DELETE(":number", api.RemoveReaction)
 		}
+
+		search := v1.Group("/search")
+		{
+			search.GET("", api.SearchForNumbers)
+		}
 	}
 
 	v2 := router.Group("/v2")