Use GitHub actions for continuous integration (arduino-libraries#26)

- On every pull request and push, compile appropriate examples for MKR1000, MKRGSM, Uno WiFi Rev2
- Comment on pull requests with a report of how the proposed changes affect memory usage
- Check all files, except the external resource src/bearssl, for commonly misspelled words. In the event of false positives, add the word (in lower case) to extras/codespell-ignore-words-list.txt.

Author: per1234

.github/workflows/compile-examples.yml

@@ -0,0 +1,76 @@
+name: Compile Examples
+
+on:
+  pull_request:
+    paths:
+      - .github/workflows/compile-examples.yml
+      - examples/**
+      - src/**
+  push:
+    paths:
+      - .github/workflows/compile-examples.yml
+      - examples/**
+      - src/**
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    env:
+      # libraries to install for all boards
+      UNIVERSAL_LIBRARIES: |
+        # install the ArduinoBearSSL library from the local path
+        - source-path: ./
+        - name: ArduinoECCX08
+      # sketch paths to compile (recursive) for all boards
+      UNIVERSAL_SKETCH_PATHS: '"examples/SHA1" "examples/SHA256"'
+
+    strategy:
+      fail-fast: false
+
+      matrix:
+        board:
+          - fqbn: arduino:samd:mkr1000
+            type: wifi101
+          - fqbn: arduino:samd:mkrgsm1400
+            type: gsm
+          - fqbn: arduino:megaavr:uno2018
+            type: megaavr
+
+        # make board type-specific customizations to the matrix jobs
+        include:
+          # WiFi101-compatible boards
+          - board:
+              type: wifi101
+            libraries: |
+              - name: WiFi101
+            sketch-paths: '"examples/WiFiSSLClient"'
+          # GSM boards
+          - board:
+              type: gsm
+            libraries: |
+              - name: MKRGSM
+            sketch-paths: '"examples/MKRGSMSSLClient"'
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Compile examples
+        uses: per1234/actions/libraries/compile-examples@beaac5ae4bb7ab294f1305e436172fde4c281fc8
+        with:
+          fqbn: ${{ matrix.board.fqbn }}
+          libraries: |
+            ${{ env.UNIVERSAL_LIBRARIES }}
+            ${{ matrix.libraries }}
+          sketch-paths: ${{ env.UNIVERSAL_SKETCH_PATHS }} ${{ matrix.sketch-paths }}
+          size-report-sketch: SHA256
+          enable-size-deltas-report: true
+          verbose: true
+
+      - name: Save sketches report as artifact
+        if: github.event_name == 'pull_request'
+        uses: actions/upload-artifact@v2
+        with:
+          name: size-deltas-reports
+          path: size-deltas-reports

.github/workflows/report-size-deltas.yml

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+name: Report Size Deltas
+
+on:
+  schedule:
+    # schedule action for every five minutes (ends up being a little longer in practice)
+    - cron: "*/5 * * * *"
+
+jobs:
+  report:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Comment size deltas reports to PRs
+        uses: arduino/actions/libraries/report-size-deltas@master

.github/workflows/spell-check.yml

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+name: Spell Check
+
+on: [push, pull_request]
+
+jobs:
+  spellcheck:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Spell check
+        uses: arduino/actions/libraries/spell-check@master
+        with:
+          ignore-words-list: extras/codespell-ignore-words-list.txt
+          skip-paths: ./extras/TrustAnchors,./src/bearssl