Add github action workflows

- All workflow are CMake based build.
- Add Workflow for Linux, macOS and Windows.
- Add workflow for C++, Python, Java, .Net.
- Update CMake/README.md.

.github/workflows/linux_python.yml

@@ -0,0 +1,24 @@
+name: Python Linux CI
+
+on: [push, pull_request]
+
+jobs:
+  # Building using the github runner environement directly.
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Check cmake
+      run: cmake --version
+    - name: Swig install
+      run: sudo apt install -y swig
+    - name: Check swig
+      run: swig -version
+    - name: Configure
+      run: cmake -S. -Bbuild -DCMAKE_BUILD_TYPE=Release -DBUILD_PYTHON=ON -DBUILD_DEPS=ON
+    - name: Build
+      run: cmake --build build --config Release --target all -v
+    - name: Test
+      run: cmake --build build --config Release --target test -v
+    - name: Install
+      run: cmake --build build --config Release --target install -v -- DESTDIR=install