Add support for debugging from VSCode

https://github.com/avajs/ava/blob/master/docs/recipes/debugging-with-vscode.md recommends passing the `debug` option to Ava.  However, in my experience Ava waits indefinitely when this option is used, without actually running any tests.

The increased timeout setting is so that tests won't fail prematurely because you're slowly stepping through code.

.vscode/launch.json

@@ -0,0 +1,25 @@
+{
+  // Use IntelliSense to learn about possible attributes.
+  // Hover to view descriptions of existing attributes.
+  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "type": "node",
+      "request": "launch",
+      "name": "Debug AVA test file",
+      "runtimeExecutable": "${workspaceFolder}/node_modules/.bin/ava",
+      "runtimeArgs": [
+        "${file}",
+        "--break",
+        "--serial",
+        "--timeout=20m"
+      ],
+      "port": 9229,
+      "outputCapture": "std",
+      "skipFiles": [
+        "<node_internals>/**/*.js"
+      ]
+    }
+  ]
+}