XXMessengerClient - logging

XXMessengerClient

• Add MessengerSetLogLevel function.
• Add MessengerStartLogging function.
• Implement logging with swift-log package.

xx-messenger example

• Log using swift-log package.
• Bootstrap logging system with Pulse library.
• Start logging when creating AppEnvironment.

Package.resolved

@@ -18,6 +18,15 @@
         "version" : "0.5.2"
       }
     },
+    {
+      "identity" : "swift-log",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-log.git",
+      "state" : {
+        "revision" : "6fe203dc33195667ce1759bf0182975e4653ba1c",
+        "version" : "1.4.4"
+      }
+    },
     {
       "identity" : "xctest-dynamic-overlay",
       "kind" : "remoteSourceControl",