Use Github Actions instead of Appveyor

.github/workflows/windows-ci.yml

@@ -0,0 +1,36 @@
+name: Windows CI
+on: [push]
+
+jobs:
+  test:
+    strategy:
+      matrix:
+        include:
+          - python_version: 3.7
+            numpy_version: numpy
+            tf_version: tensorflow
+            nengo_version: nengo[tests]
+          - python_version: 3.8
+            numpy_version: numpy
+            tf_version: tensorflow --pre
+            nengo_version: git+https://github.com/nengo/nengo.git#egg=nengo[tests]
+          - python_version: 3.6
+            numpy_version: numpy==1.16.0
+            tf_version: tensorflow==2.2.0
+            nengo_version: nengo[tests]==3.0.0
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python_version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install pip setuptools --upgrade
+          pip install ${{ matrix.numpy_version }} ${{ matrix.tf_version }} ${{ matrix.nengo_version }}
+          pip install -e .[tests]
+          pip freeze
+      - name: Run tests
+        run: |
+          pytest -n 2 -v --durations 20 nengo_dl
+          pytest -n 2 -v --durations 20 --pyargs nengo