Only trigger AppVeyor on code or config changes (GH-611)

Author: zware

.github/appveyor.yml

@@ -4,3 +4,20 @@ build_script:
 - cmd: PCbuild\build.bat -e
 test_script:
 - cmd: PCbuild\rt.bat -q -uall -rwW --slowest --timeout=1200 -j0
+
+# Only trigger AppVeyor if actual code or its configuration changes
+only_commits:
+  files:
+    - .github/appveyor.yml
+    - .gitattributes
+    - Grammar/
+    - Include/
+    - Lib/
+    - Modules/
+    - Objects/
+    - PC/
+    - PCBuild/
+    - Parser/
+    - Programs/
+    - Python/
+    - Tools/