Add JSON formatter

lib/grape_logging/formatters/json.rb

@@ -0,0 +1,33 @@
+module GrapeLogging
+  module Formatters
+    class Json
+      def call(severity, datetime, _, data)
+        JSON.parse({
+          date: datetime,
+          severity: severity,
+          data: format(data)
+        })
+      end
+
+      private
+
+      def format(data)
+        if data.is_a?(String) || data.is_a?(Hash)
+          data
+        elsif data.is_a?(Exception)
+          format_exception(data)
+        else
+          data.inspect
+        end
+      end
+
+      def format_exception(exception)
+        {
+          exception: {
+            message: exception.message
+          }
+        }
+      end
+    end
+  end
+end