ci: Add docker based test framework

* Add documentation
* Add .dockerignore: minimize docker context size to improve speed
* Add Makefile: to easily run various docker stages
* Add a CMake sample project to check CMake install rules

ci/sample/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.15)
+project(Sample VERSION 1.0.0 LANGUAGES CXX)
+
+include(CTest)
+find_package(CpuFeatures REQUIRED)
+
+add_executable(sample main.cpp)
+target_compile_features(sample PUBLIC cxx_std_11)
+set_target_properties(sample PROPERTIES
+  CXX_STANDARD 11
+  CXX_STANDARD_REQUIRED ON
+  VERSION ${PROJECT_VERSION})
+target_link_libraries(sample PRIVATE CpuFeatures::cpu_features)
+
+if(BUILD_TESTING)
+  add_test(NAME sample_test COMMAND sample)
+endif()
+
+include(GNUInstallDirs)
+install(TARGETS sample
+  EXPORT SampleTargets
+  DESTINATION ${CMAKE_INSTALL_BIN_DIR})

ci/sample/main.cpp

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+#include <iostream>
+
+#include "cpuinfo_x86.h"
+
+using namespace cpu_features;
+
+int main(int /*argc*/, char** /*argv*/) {
+  static const X86Features features = GetX86Info().features;
+  std::cout << std::endl;
+  return 0;
+}