Deprecate callbacks

Nothing of what the callbacks offered couldn't be done by custom
printers/outputs. Removing the callbacks simplifies the code.

Author: haarts

lib/src/logger.dart

@@ -33,7 +33,10 @@ class OutputEvent {
   OutputEvent(this.level, this.lines);
 }
 
+@Deprecated("Use a custom LogFilter instead")
 typedef LogCallback = void Function(LogEvent event);
+
+@Deprecated("Use a custom LogOutput instead")
 typedef OutputCallback = void Function(OutputEvent event);
 
 /// Use instances of logger to send log messages to the [LogPrinter].
@@ -43,7 +46,9 @@ class Logger {
   /// All logs with levels below this level will be omitted.
   static Level level = Level.verbose;
 
+  // NOTE: callbacks are soon to be removed
   static final Set<LogCallback> _logCallbacks = Set();
+  // NOTE: callbacks are soon to be removed
   static final Set<OutputCallback> _outputCallbacks = Set();
 
   final LogFilter _filter;
@@ -112,13 +117,15 @@ class Logger {
     }
     var logEvent = LogEvent(level, message, error, stackTrace);
     if (_filter.shouldLog(logEvent)) {
+      // NOTE: callbacks are soon to be removed
       for (var callback in _logCallbacks) {
         callback(logEvent);
       }
       var output = _printer.log(logEvent);
 
       if (output.isNotEmpty) {
         var outputEvent = OutputEvent(level, output);
+        // NOTE: callbacks are soon to be removed
         for (var callback in _outputCallbacks) {
           callback(outputEvent);
         }
@@ -136,25 +143,29 @@ class Logger {
   }
 
   /// Register a [LogCallback] which is called for each new [LogEvent].
+  @Deprecated("Use a custom LogFilter instead")
   static void addLogListener(LogCallback callback) {
     _logCallbacks.add(callback);
   }
 
   /// Removes a [LogCallback] which was previously registered.
   ///
   /// Returns wheter the callback was successfully removed.
+  @Deprecated("Use a custom LogFilter instead")
   static bool removeLogListener(LogCallback callback) {
     return _logCallbacks.remove(callback);
   }
 
   /// Register an [OutputCallback] which is called for each new [OutputEvent].
+  @Deprecated("Use a custom LogOutput instead")
   static void addOutputListener(OutputCallback callback) {
     _outputCallbacks.add(callback);
   }
 
   /// Removes a [OutputCallback] which was previously registered.
   ///
   /// Returns wheter the callback was successfully removed.
+  @Deprecated("Use a custom LogOutput instead")
   static void removeOutputListener(OutputCallback callback) {
     _outputCallbacks.remove(callback);
   }