added .codecov.yml, adjusted `make coverage`

Signed-off-by: bigcat88 <bigcat88@icloud.com>

.github/.codecov.yml

@@ -0,0 +1,14 @@
+comment:
+  require_changes: true
+  layout: "diff, files"
+
+coverage:
+  status:
+    project:
+      default:
+        target: auto
+        threshold: 2%
+    patch:
+      default:
+        target: auto
+        threshold: 2%

Makefile

@@ -81,7 +81,7 @@ l10n:
 
 .PHONY: coverage
 coverage:
-	$(coverage) html
+	$(coverage) html && $(coverage) xml
 
 .PHONY: test-user
 test-user: