add: github actions

.github/workflows/build.yaml

@@ -0,0 +1,39 @@
+name: apertium-python CI Build
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install pipenv
+        python3 setup.py install
+        pipenv install --dev --system
+    - name: Flake8 checks
+      run: |
+        flake8 --verbose apertium
+    - name: mypy checks
+      run: |
+        mypy apertium --strict --any-exprs-report .mypy_coverage --ignore-missing-imports
+        cat .mypy_coverage/any-exprs.txt
+        coverage=$(tail -1 .mypy_coverage/any-exprs.txt | grep -Eo '[0-9\.]+%' | sed 's/%$//')
+        if (( $(echo "$coverage < 95" | bc -l) )); then
+            exit 1
+        fi
+    - name: code coverage and unittest
+      run: |
+        coverage run -m unittest --verbose --buffer tests
+        coverage report --show-missing --fail-under 90 --include 'apertium/*'