add rapidjson from cmake (direct download rapidjson in CMake)

TwoFilesInONe.CMAKE

# Download RapidJSON 
ExternalProject_Add(
    rapidjson
    PREFIX "vendor/rapidjson"
    GIT_REPOSITORY "https://github.com/Tencent/rapidjson.git"
    GIT_TAG f54b0e47a08782a6131cc3d60f94d038fa6e0a51
    TIMEOUT 10
    CMAKE_ARGS
        -DRAPIDJSON_BUILD_TESTS=OFF
        -DRAPIDJSON_BUILD_DOC=OFF
        -DRAPIDJSON_BUILD_EXAMPLES=OFF
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND ""
    UPDATE_COMMAND ""
)

# Prepare RapidJSON (RapidJSON is a header-only library)
ExternalProject_Get_Property(rapidjson source_dir)
set(RAPIDJSON_INCLUDE_DIR ${source_dir}/include)



# use case (Parent CMake):
include("${CMAKE_SOURCE_DIR}/vendor/rapidjson.cmake")

include_directories(
    ${CMAKE_SOURCE_DIR}/include
    ${GFLAGS_INCLUDE_DIR}
    ${BENCHMARK_INCLUDE_DIR}
    ${RAPIDJSON_INCLUDE_DIR}
)