Adds gitlens.diffWithPrevious command to the explore context menu

Adds output channel logging, controlled by the `gitlens.advanced.output.level` setting
Removes all debug logging, unless the `gitlens.advanced.output.debug` settings it on

src/logger.ts

@@ -0,0 +1,57 @@
+'use strict';
+import { Objects } from './system';
+import { OutputChannel, window, workspace } from 'vscode';
+import { IAdvancedConfig, OutputLevel } from './configuration';
+
+let config: IAdvancedConfig;
+let output: OutputChannel;
+
+workspace.onDidChangeConfiguration(onConfigurationChange);
+onConfigurationChange();
+
+function onConfigurationChange() {
+    const cfg = workspace.getConfiguration('gitlens').get<IAdvancedConfig>('advanced');
+
+    if (!Objects.areEquivalent(cfg.output, config && config.output)) {
+        if (cfg.output.level === OutputLevel.Silent) {
+            output && output.dispose();
+        }
+        else if (!output) {
+            output = window.createOutputChannel('GitLens');
+        }
+    }
+
+    config = cfg;
+}
+
+export class Logger {
+    static log(message?: any, ...params: any[]): void {
+        if (config.output.debug) {
+            console.log('[GitLens]', message, ...params);
+        }
+
+        if (config.output.level === OutputLevel.Verbose) {
+            output.appendLine([message, ...params].join(' '));
+        }
+    }
+
+    static error(message?: any, ...params: any[]): void {
+        if (config.output.debug) {
+            console.error('[GitLens]', message, ...params);
+        }
+
+        if (config.output.level !== OutputLevel.Silent) {
+            output.appendLine([message, ...params].join(' '));
+        }
+    }
+
+    static warn(message?: any, ...params: any[]): void {
+        if (config.output.debug) {
+            console.warn('[GitLens]', message, ...params);
+        }
+
+        if (config.output.level !== OutputLevel.Silent) {
+            output.appendLine([message, ...params].join(' '));
+        }
+    }
+}