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

util/src/lib.rs

@@ -26,10 +26,8 @@ extern crate base64;
 extern crate byteorder;
 extern crate rand;
 #[macro_use]
-extern crate slog;
-extern crate slog_async;
-extern crate slog_term;
-
+extern crate log;
+extern crate log4rs;
 #[macro_use]
 extern crate lazy_static;
 
@@ -48,7 +46,7 @@ pub extern crate secp256k1zkp as secp;
 
 // Logging related
 pub mod logger;
-pub use logger::{init_logger, init_test_logger, LOGGER};
+pub use logger::{init_logger, init_test_logger};
 
 // Static secp instance
 pub mod secp_static;