Runtime logging. (#3821)

* Implement Printable for tuples.

* Add debugging function.

* Add debug 1.

* Implement  for everything.

* RuntimeDebug derive.

* Introduce RuntimeDebug.

* Add some dummy logging.

* Replace RuntimeDebug with Debug.

* Revert "Replace RuntimeDebug with Debug."

This reverts commit bc47070a8cb30241b2b590b2fa29fd195088162f.

* Working on Debug for all.

* Fix bounds.

* Add debug utils.

* Implement runtime logging.

* Add some docs and clean up.

* Clean up derives.

* Fix custom derive impl.

* Bump runtime.

* Fix long lines.

* Fix doc test.

* Use CARGO_CFG_STD.

* Revert "Use CARGO_CFG_STD."

This reverts commit ea429566de18ed0fa052571b359eb9826a64a9f4.

* Use parse_macro_input

* Update lockfile.

* Apply review suggestions.

* Remove stray re-export.

* Add no-std impl.

* Update lockfile.

substrate/core/sr-io/without_std.rs

@@ -160,6 +160,14 @@ pub mod ext {
 		fn ext_print_hex(data: *const u8, len: u32);
 		/// Print a number
 		fn ext_print_num(value: u64);
+		/// Print a log line if logging for given level and target is enabled.
+		fn ext_log(
+			level: u32,
+			target_data: *const u8,
+			target_len: u32,
+			message_data: *const u8,
+			message_len: u32,
+		);
 
 		/// Set value for key in storage.
 		fn ext_set_storage(key_data: *const u8, key_len: u32, value_data: *const u8, value_len: u32);
@@ -780,6 +788,22 @@ impl OtherApi for () {
 			ext_print_hex.get()(data.as_ptr(), data.len() as u32);
 		}
 	}
+
+	fn log(
+		level: LogLevel,
+		target: &[u8],
+		message: &[u8]
+	) {
+		unsafe {
+			ext_log.get()(
+				level as u32,
+				target.as_ptr(),
+				target.len() as u32,
+				message.as_ptr(),
+				message.len() as u32,
+			)
+		}
+	}
 }
 
 impl HashingApi for () {