Refactor query routing into its own module (#22)

* Refactor query routing into its own module

* commments; tests; dead code

* error message

* safer startup

* hm

* dont have to be public

* wow

* fix ci

* ok

* nl

* no more silent errors

tests/sharding/query_routing_test_validate.sql

@@ -8,4 +8,4 @@ SELECT * FROM data;
 
 \c shard2
 
-SELECT * FROM data;
+SELECT * FROM data;