Add C/C++ with CMake GitHub workflow

This enables continuous integration
with GitHub Actions.

.github/workflows/ccppcmake.yml

@@ -0,0 +1,32 @@
+name: C/C++ CI with CMake
+
+on: [push]
+
+env:
+  BUILD_TYPE: Release
+  CMAKE_VERSION: 3.15.2
+
+jobs:
+  build:
+  
+    runs-on: ubuntu-latest
+    
+    steps:
+    - uses: actions/checkout@v1
+    - name: Install dependencies
+      shell: bash
+      working-directory: ${{runner.workspace}}
+      run: | # Fetch a new version of CMake, because the default is too old.
+           wget -nv https://github.com/Kitware/CMake/releases/download/v$CMAKE_VERSION/cmake-$CMAKE_VERSION-Linux-x86_64.tar.gz \
+           && tar -zxf cmake-$CMAKE_VERSION-Linux-x86_64.tar.gz \
+           && sudo apt-get install gtk+-3.0 libcurl4-gnutls-dev libpcap0.8-dev libsdl2-dev
+    - name: Create build environment
+      run: mkdir ${{runner.workspace}}/build
+    - name: Configure
+      shell: bash
+      working-directory: ${{runner.workspace}}/build
+      run: ${{runner.workspace}}/cmake-$CMAKE_VERSION-Linux-x86_64/bin/cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE
+    - name: Make
+      shell: bash
+      working-directory: ${{runner.workspace}}/build
+      run: make -j$(nproc --all)