0a340c6d71
Add options to link against external JSON libraries This adds two options to the CMake config: `CPPDAP_USE_EXTERNAL_NLOHMANN_JSON_PACKAGE` and `CPPDAP_USE_EXTERNAL_RAPIDJSON_PACKAGE` If either of these is set, instead of using the json submodule, the build will be configured by using `find_package()` and linking against the specified JSON library.