Move src/logger.rs into logger/ crate to unify logging across the workspace

logger/src/lib.rs

@@ -0,0 +1,16 @@
+//! The `logger` module provides a setup function for `env_logger`. Its only function,
+//! `setup()` may be called multiple times.
+
+use env_logger;
+use std::sync::{Once, ONCE_INIT};
+
+static INIT: Once = ONCE_INIT;
+
+/// Setup function that is only run once, even if called multiple times.
+pub fn setup() {
+    INIT.call_once(|| {
+        env_logger::Builder::from_default_env()
+            .default_format_timestamp_nanos(true)
+            .init();
+    });
+}