Only turn on tokio features that are used by this crate (#10)

Cargo.toml

@@ -12,7 +12,7 @@ license = "Apache-2.0"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-tokio = { version = "1.5.0", features = ["full"] }
+tokio = { version = "1.5.0", features = ["macros", "rt-multi-thread", "sync", "time"] }
 futures = "0.3.14"
 thiserror = "1.0"