Set up CI using GitHub Actions

This ports our Travis CI setup to GitHub Actions, and also adds CI for
Python 3.8 and 3.9. 3.10 was not added as it is broken due to deprecated
'#' formats. 3.4 was dropped as it's not available on Ubuntu 20.04.

Author: robinlinden

.github/workflows/ci.yml

@@ -0,0 +1,79 @@
+name: ci
+
+on:
+  pull_request:
+    branches: [master]
+
+jobs:
+  build:
+    name: python-${{ matrix.version }}
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        include:
+        - version: "2.7"
+        - version: "3.5"
+        - version: "3.6"
+        - version: "3.8"
+        - version: "3.9"
+        # TODO(robinlinden): Fix PY_SSIZE_T_CLEAN errors.
+        # - version: "3.10"
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.version }}
+    - name: Install
+      run: |
+        sudo apt update
+        sudo apt install -y --no-install-recommends --no-install-suggests libtoxcore-dev
+    - name: Build
+      run: python setup.py build_ext --inplace
+    - name: Test
+      run: PYTHONPATH=. python tests/tests.py
+
+  coverage:
+    name: python-3.7-coverage
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-python@v2
+      with:
+        python-version: "3.7"
+    - name: Install
+      run: |
+        sudo apt update
+        sudo apt install -y --no-install-recommends --no-install-suggests libtoxcore-dev
+    - name: Build
+      run: |
+        export CFLAGS="-fprofile-arcs -ftest-coverage"
+        python setup.py build_ext --inplace
+    - name: Test
+      run: PYTHONPATH=. python tests/tests.py
+    - name: Upload coverage
+      run: bash <(curl -s https://codecov.io/bash)
+
+  docker:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build
+      run: docker build -t pytox .
+
+  clang-analyze:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install
+      run: |
+        sudo apt update
+        sudo apt install -y --no-install-recommends --no-install-suggests libtoxcore-dev
+    - name: Build
+      run: |
+        clang -fsyntax-only pytox/*.c -Werror -Weverything -Wno-reserved-id-macro -Wno-documentation-deprecated-sync -Wno-shorten-64-to-32 -Wno-unused-parameter -Wno-missing-field-initializers -Wno-sign-conversion -Wno-padded -Wno-conversion $(pkg-config --cflags-only-I python3)
+        clang --analyze pytox/*.c $(pkg-config --cflags-only-I python3)