Support Python 3.10 and Drop Python 3.5 (#487)

* linux: Use manylinux2014
* mac: Drop Python 3.6 too

.github/workflows/linux.yml

@@ -47,6 +47,17 @@ jobs:
           pytest -v test
 
 
+      - name: Set up Python 3.10
+        uses: actions/setup-python@v1
+        with:
+          python-version: "3.10"
+
+      - name: Run test (3.10)
+        run: |
+          pip install pytest
+          pip install -v msgpack --only-binary :all: --no-index -f dist/wheelhouse
+          pytest -v test
+
       - name: Set up Python 3.9
         uses: actions/setup-python@v1
         with: