Automatically download Runge-Kutta on build

[krystophny]

example cmake:

include(ExternalProject)

# Define the URL of the file you want to download
set(FILE_URL "https://example.com/path/to/your/file.zip")

# Define where you want to extract the downloaded file
set(EXTRACT_DIR "${CMAKE_BINARY_DIR}/extracted")

# Create an ExternalProject target to download and extract the file
ExternalProject_Add(
    my_download_and_extract_target
    PREFIX ${CMAKE_BINARY_DIR}/download
    URL ${FILE_URL}
    URL_HASH SHA256=<insert_sha256_hash_of_file_here>
    DOWNLOAD_DIR ${CMAKE_BINARY_DIR}/download
    DOWNLOAD_NO_PROGRESS 1
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND ${CMAKE_COMMAND} -E tar xzf <DOWNLOADED_FILE> -C ${EXTRACT_DIR}
    BUILD_IN_SOURCE 1
)

# Add a custom target that depends on the download and extract target
add_custom_target(download_and_extract
    DEPENDS my_download_and_extract_target
)