add CI workflow to build library and examples (and pray)

.github/workflows/workflow.yml

@@ -0,0 +1,56 @@
+name: PlatformIO CI
+
+on: [push]
+
+jobs:
+  build_and_test:
+
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        examples: [
+            examples/accelmaggyro.cpp,
+            examples/accgyro.cpp,
+            examples/accmag.cpp,
+            examples/acconly.cpp,
+            examples/euler.cpp,
+            examples/gyroonly.cpp,
+            examples/maggyro.cpp,
+            examples/magonly.cpp,
+            examples/quaternion.cpp,
+            examples/interrupts/accelAnyMotionInterrupt.cpp,
+            examples/interrupts/accelHighGInterrupt.cpp,
+            examples/interrupts/gyroAnyMotionInterrupt.cpp,
+            examples/interrupts/gyroHighRateInterrupt.cpp,
+            examples/interrupts/noMotionInterrupt.cpp,
+            examples/interrupts/slowMotionInterrupt.cpp
+        ]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Cache pip
+        uses: actions/cache@v2
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
+      - name: Cache PlatformIO
+        uses: actions/cache@v2
+        with:
+          path: ~/.platformio
+          key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+
+      - name: Install PlatformIO
+        run: |
+          python -m pip install --upgrade pip
+          pip install --upgrade platformio
+
+      - name: Run PlatformIO
+        run: pio ci --lib "." --board teensy41
+        env:
+          PLATFORMIO_CI_SRC: ${{ matrix.examples }}