Add support for multiple database instances #53

Job	Run time
fmt	8s
doc	1m 21s
test	47s
clippy (runtime-tokio-native-tls, no-db w/o any)	22s
clippy (runtime-tokio-rustls, no-db w/o any)	34s
clippy (runtime-tokio-native-tls, all-databases w/o any)	41s
clippy (runtime-tokio-rustls, all-databases w/o any)	42s
clippy (runtime-tokio-native-tls, mysql w/o any)	44s
clippy (runtime-tokio-rustls, mysql w/o any)	28s
clippy (runtime-tokio-native-tls, mysql w/ any)	36s
clippy (runtime-tokio-rustls, mysql w/ any)	1m 0s
clippy (runtime-tokio-native-tls, postgres w/o any)	29s
clippy (runtime-tokio-rustls, postgres w/o any)	30s
clippy (runtime-tokio-native-tls, postgres w/ any)	36s
clippy (runtime-tokio-rustls, postgres w/ any)	37s
clippy (runtime-tokio-native-tls, sqlite w/o any)	56s
clippy (runtime-tokio-rustls, sqlite w/o any)	1m 5s
clippy (runtime-tokio-native-tls, sqlite w/ any)	28s
clippy (runtime-tokio-rustls, sqlite w/ any)	59s
	13m 3s

Provide feedback