add Python 3.10 to CI testing and binary wheels

A Python 3.10 binary wheel for v0.2.1 of this library will be pushed to
PyPI from this commit.

.github/workflows/maturin_build_wheel.py

@@ -23,6 +23,7 @@
         (3, 7): "cp37-cp37m",
         (3, 8): "cp38-cp38",
         (3, 9): "cp39-cp39",
+        (3, 10): "cp310-cp310",
         # This list needs to be kept in sync with push.yml and tag.yml.
     }
     version_component = version_path_components[sys.version_info[:2]]

.github/workflows/push.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.platform.os }}
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9] # This list needs to be kept in sync with tag.yml and maturin_build_wheel.py.
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"] # This list needs to be kept in sync with tag.yml and maturin_build_wheel.py.
         rust-toolchain: [stable, beta, nightly]
         platform: [
           # This list should be kept in sync with tag.yml.

.github/workflows/tag.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.platform.os }}
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9] # This list needs to be kept in sync with push.yml and maturin_build_wheel.py.
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"] # This list needs to be kept in sync with push.yml and maturin_build_wheel.py.
         platform: [
           # This list should be kept in sync with push.yml.
           { os: "ubuntu-latest",  python-architecture: "x64", rust-target: "x86_64-unknown-linux-gnu", name: "Linux x64" },