Switch from appveyor to GH actions for Windows tests

Author: adamtheturtle

.appveyor.yml

@@ -15,11 +15,12 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
-
     strategy:
       matrix:
         python-version: [3.7, 3.8]
+        platform: [ubuntu-latest, windows-latest]
+
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v2