Only fail if code coverage drops by over 0.5%

Currently codecov, annoyingly, fails the PR whenever coverage decreases.

This commit changes the threshold, and will only fail PRs if:
- coverage falls below 80%
- coverage drops by more than 0.5%

.codecov.yml

@@ -13,8 +13,11 @@ coverage:
   round: down
   status:
     changes: false
-    patch: true
-    project: true
+    patch: false
+    project: 
+      target: 80
+      threshold: 0.5
+      base: pr
 parsers:
   gcov:
     branch_detection: