externals: Add JSON as a submodule.

.gitmodules

@@ -31,3 +31,6 @@
 [submodule "cpr"]
     path = externals/cpr
     url = https://github.com/whoshuu/cpr.git
+[submodule "json"]
+    path = externals/json
+    url = https://github.com/nlohmann/json.git

externals/CMakeLists.txt

@@ -34,6 +34,10 @@ add_subdirectory(glad)
 # inih
 add_subdirectory(inih)
 
+# JSON
+add_library(json-headers INTERFACE)
+target_include_directories(json-headers INTERFACE ./json/src)
+
 # MicroProfile
 add_library(microprofile INTERFACE)
 target_include_directories(microprofile INTERFACE ./microprofile)

externals/json

@@ -0,0 +1 @@
+Subproject commit d3496347fcd1382896fca3aaf78a0d803c2f52ec