Added log level comparison operators

Author: busslina

lib/src/filters/development_filter.dart

@@ -10,7 +10,7 @@ class DevelopmentFilter extends LogFilter {
   bool shouldLog(LogEvent event) {
     var shouldLog = false;
     assert(() {
-      if (event.level.value >= level!.value) {
+      if (event.level >= level!) {
         shouldLog = true;
       }
       return true;

lib/src/filters/production_filter.dart

@@ -5,6 +5,6 @@ import '../log_filter.dart';
 class ProductionFilter extends LogFilter {
   @override
   bool shouldLog(LogEvent event) {
-    return event.level.value >= level!.value;
+    return event.level >= level!;
   }
 }

lib/src/log_level.dart

@@ -20,4 +20,12 @@ enum Level {
   final int value;
 
   const Level(this.value);
+
+  bool operator <(Level other) => value < other.value;
+
+  bool operator <=(Level other) => value <= other.value;
+
+  bool operator >(Level other) => value > other.value;
+
+  bool operator >=(Level other) => value >= other.value;
 }