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

api/Cargo.toml

@@ -15,7 +15,7 @@ ring = "0.13"
 serde = "1"
 serde_derive = "1"
 serde_json = "1"
-slog = { version = "~2.3", features = ["max_level_trace", "release_max_level_trace"] }
+log = "0.4"
 tokio = "0.1.7"
 tokio-core = "0.1.17"
 tokio-tcp = "0.1"