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" }

pool/src/lib.rs

@@ -30,7 +30,7 @@ extern crate serde;
 #[macro_use] // Needed for Serialize/Deserialize. The compiler complaining here is a bug.
 extern crate serde_derive;
 #[macro_use]
-extern crate slog;
+extern crate log;
 extern crate chrono;
 
 mod pool;

pool/src/pool.rs

@@ -26,7 +26,6 @@ use core::core::transaction;
 use core::core::verifier_cache::VerifierCache;
 use core::core::{Block, BlockHeader, BlockSums, Committed, Transaction, TxKernel};
 use types::{BlockChain, PoolEntry, PoolEntryState, PoolError};
-use util::LOGGER;
 
 // max weight leaving minimum space for a coinbase
 const MAX_MINEABLE_WEIGHT: usize =
@@ -192,7 +191,6 @@ impl Pool {
 		header: &BlockHeader,
 	) -> Result<(), PoolError> {
 		debug!(
-			LOGGER,
 			"pool [{}]: add_to_pool: {}, {:?}, inputs: {}, outputs: {}, kernels: {} (at block {})",
 			self.name,
 			entry.tx.hash(),