Replace logging backend to log4rs and add log rotation (#1789)

* Replace logging backend to flexi-logger and add log rotation
* Changed flexi_logger to log4rs
* Disable logging level filtering in Root logger
* Support different logging levels for file and stdout
* Don't log messages from modules other than Grin-related
* Fix formatting
* Place backed up compressed log copies into log file directory
* Increase default log file size to 16 MiB
* Add comment to config file on log_max_size option

pool/Cargo.toml

@@ -10,7 +10,7 @@ blake2-rfc = "0.2"
 rand = "0.5"
 serde = "1"
 serde_derive = "1"
-slog = { version = "~2.3", features = ["max_level_trace", "release_max_level_trace"] }
+log = "0.4"
 chrono = "0.4.4"
 
 grin_core = { path = "../core" }