Reorganize directories (#3462)

* 🚚 move files
* 🚚 rename doc folder to docs
* 🚚 rename test folder to tests

tests/cuda_example/CMakeLists.txt

@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 3.18)
+project(json_cuda LANGUAGES CUDA)
+
+add_executable(json_cuda json_cuda.cu)
+target_include_directories(json_cuda PRIVATE ../../include)
+target_compile_features(json_cuda PUBLIC cuda_std_11)
+set_target_properties(json_cuda PROPERTIES
+    CUDA_EXTENSIONS OFF
+    CUDA_STANDARD_REQUIRED ON
+)

tests/cuda_example/json_cuda.cu

@@ -0,0 +1,11 @@
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_json json = {"Test"};
+    json.dump();
+
+    // regression for #3013 (ordered_json::reset() compile error with nvcc)
+    nlohmann::ordered_json metadata;
+    metadata.erase("key");
+}