Use Github Actions for CI (bsamseth#19)

The current workflow does less than Travis/Appveyor, but serves as a nice and simple way to do CI with zero setup. Can/should be expanded to do more.

.github/workflows/ci.yml

@@ -0,0 +1,51 @@
+name: CI
+
+on: [push]
+
+jobs:
+  build-ubuntu:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Checkout submodules
+      shell: bash
+      run: |
+        auth_header="$(git config --local --get http.https://github.com/.extraheader)"
+        git submodule sync --recursive
+        git -c "http.extraheader=$auth_header" -c protocol.version=2 submodule update --init --force --recursive --depth=1
+        
+    - name: configure
+      run: mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=debug ..
+    - name: build
+      run: cmake --build build
+    - name: test
+      run: cd build && ctest
+
+
+  build-windows:
+
+    runs-on: windows-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Checkout submodules
+      shell: bash
+      run: |
+        auth_header="$(git config --local --get http.https://github.com/.extraheader)"
+        git submodule sync --recursive
+        git -c "http.extraheader=$auth_header" -c protocol.version=2 submodule update --init --force --recursive --depth=1
+        
+    - name: configure
+      run: |
+        mkdir build
+        cd build
+        cmake ..
+    - name: build
+      run: cmake --build build
+    - name: test
+      run: |
+        cd build
+        set CTEST_OUTPUT_ON_FAILURE=1
+        ctest -C Debug