Enable python 3.11 support, and remove 3.6 support. (#256)

* Update CI to use 3.11

Fixes #255

Author: gordonwatts

.github/workflows/ci.yaml

@@ -40,7 +40,7 @@ jobs:
     strategy:
       matrix:
         platform: [ubuntu-latest, windows-latest]
-        python-version: [3.7, 3.8, 3.9, "3.10"]
+        python-version: [3.7, 3.8, 3.9, "3.10", "3.11"]
     runs-on: ${{ matrix.platform }}
 
     steps: