Convert logger to typescript

Because it's annoying for the IDE to have no idea what methods are
on the logger. `loglevel` has types so it should just pass them
through.

src/logger.ts

@@ -0,0 +1,59 @@
+/*
+Copyright 2018 André Jaenisch
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * @module logger
+ */
+
+import log from "loglevel";
+
+// This is to demonstrate, that you can use any namespace you want.
+// Namespaces allow you to turn on/off the logging for specific parts of the
+// application.
+// An idea would be to control this via an environment variable (on Node.js).
+// See https://www.npmjs.com/package/debug to see how this could be implemented
+// Part of #332 is introducing a logging library in the first place.
+const DEFAULT_NAMESPACE = "matrix";
+
+// because rageshakes in react-sdk hijack the console log, also at module load time,
+// initializing the logger here races with the initialization of rageshakes.
+// to avoid the issue, we override the methodFactory of loglevel that binds to the
+// console methods at initialization time by a factory that looks up the console methods
+// when logging so we always get the current value of console methods.
+log.methodFactory = function(methodName, logLevel, loggerName) {
+    return function(...args) {
+        const supportedByConsole = methodName === "error" ||
+            methodName === "warn" ||
+            methodName === "trace" ||
+            methodName === "info";
+        /* eslint-disable no-console */
+        if (supportedByConsole) {
+            return console[methodName](...args);
+        } else {
+            return console.log(...args);
+        }
+        /* eslint-enable no-console */
+    };
+};
+
+/**
+ * Drop-in replacement for <code>console</code> using {@link https://www.npmjs.com/package/loglevel|loglevel}.
+ * Can be tailored down to specific use cases if needed.
+ */
+export const logger = log.getLogger(DEFAULT_NAMESPACE);
+logger.setLevel(log.levels.DEBUG);
+