switch from log to tracing

I think this is a big improvement in readability.

I removed the `lnav` config, which is a little sad, but I don't think it
supports this structured logging format well. Still seems worthwhile on
balance.

server/db/recording.rs

@@ -7,9 +7,9 @@
 use crate::coding::{append_varint32, decode_varint32, unzigzag32, zigzag32};
 use crate::db;
 use failure::{bail, Error};
-use log::trace;
 use std::convert::TryFrom;
 use std::ops::Range;
+use tracing::trace;
 
 pub use base::time::TIME_UNITS_PER_SEC;