add logging functionality for aligning key value pairs after message (#461)

* add logging functionality for aligning key value pairs after the main messages

* move to own crate, change default message width to 40

* use FullFormat in validator_client (CompactFormat is not compatible with aligning)

* move logging to eth2/utils/logging

beacon_node/src/main.rs

@@ -173,6 +173,7 @@ fn main() {
 
     // build the initial logger
     let decorator = slog_term::TermDecorator::new().build();
+    let decorator = logging::AlignedTermDecorator::new(decorator, logging::MAX_MESSAGE_WIDTH);
     let drain = slog_term::FullFormat::new(decorator).build().fuse();
     let drain = slog_async::Async::new(drain).build();