Add gdb debugging capability

.vscode/launch.json

@@ -0,0 +1,18 @@
+{
+    // 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": [
+
+        {
+            "name": "Nim Debug",
+            "type": "gdb",
+            "request": "launch",
+            "target": "${workspaceFolder}\\build\\demo\\demo_glfw_debug.exe",
+            "cwd": "${workspaceRoot}",
+            "gdbpath": "${workspaceFolder}\\nim-gdb.bat",
+            "valuesFormatting": "parseText"
+        }
+    ]
+}