libragephoto: C++ headers have now .hpp extension

RagePhoto.h -> RagePhoto.hpp
RagePhotoA.h -> RagePhotoA.hpp
RagePhotoC.h -> RagePhoto.h

unicode.cmake: exclude codecvt for C builds
GitHub Actions: separate C and CXX builds

.github/workflows/ubuntu-cxx.yml

@@ -0,0 +1,29 @@
+name: Ubuntu CXX
+
+on: push
+
+jobs:
+  Release:
+    runs-on: ubuntu-latest
+    env:
+      BUILD_TYPE: Release
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: recursive
+    - name: Install packages
+      run: |
+        sudo apt-get update -qq
+        sudo apt-get install cmake gcc g++ ninja-build -qq
+    - name: Configure CMake
+      run: cmake -B ${{github.workspace}}/build -DCMAKE_CXX_STANDARD=17 -DCMAKE_BUILD_TYPE=${{env.BUILD_TYPE}} -GNinja
+    - name: Build
+      run: cmake --build ${{github.workspace}}/build --config ${{env.BUILD_TYPE}}
+    - name: Install
+      run: cmake --install ${{github.workspace}}/build --config ${{env.BUILD_TYPE}} --prefix ${{github.workspace}}/install/usr/local
+    - name: Upload
+      uses: actions/upload-artifact@v2
+      with:
+        name: Ubuntu
+        path: |
+          ${{github.workspace}}/install/