Prepare CLI for move into mainline

packages/cli/examples/plugin/interface.lua

@@ -0,0 +1,25 @@
+local interface = {}
+
+if plugin_logger ~= nil then
+    interface.log = plugin_logger
+else
+    interface.log = {
+        trace = function (info)
+            print("trace: " .. info)
+        end,
+        debug = function (info)
+            print("debug: " .. info)
+        end,
+        info = function (info)
+            print("info: " .. info)
+        end,
+        warn = function (info)
+            print("warn: " .. info)
+        end,
+        error = function (info)
+            print("error: " .. info)
+        end,
+    }
+end
+
+return interface