Introduce conversion functions that reify retriers
Introduce conversion functions that reify resolvers and mutations
Rename default-retrier to counting-retrier
Facepalm
Integrate retriers into welle.kv/store, /fetch and /fetch-one
Integrate retriers into welle.kv/delete and /index-query

index-query currently does not take any options and using the default
retrier is probably OK for now