chore: Add PlatformIO workflow to run examples

.github/workflows/platformio.yml

@@ -0,0 +1,53 @@
+name: PlatformIO CI
+
+on: [push]
+
+jobs:
+  platformio:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        example:
+          - examples/AltPinSerial
+          - examples/Basic_IO
+          - examples/Bench
+          - examples/Callbacks
+          - examples/DualMerger
+          - examples/ErrorCallback
+          - examples/Input
+          - examples/RPN_NRPN
+          - examples/SimpleSynth
+    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="uno"               \
+        --board="due"               \
+        --board="zero"              \
+        --board="leonardo"          \
+        --board="micro"             \
+        --board="nanoatmega328"     \
+        --board="megaatmega2560"    \
+        --board="teensy2"           \
+        --board="teensy30"          \
+        --board="teensy31"          \
+        --board="teensylc"
+      env:
+        PLATFORMIO_CI_SRC: ${{ matrix.example }}