Meta+CMake: Convert JSON library from git submodule to system package

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "vendor/json"]
-	path = vendor/json
-	url = https://github.com/nlohmann/json

CMakeLists.txt

@@ -56,7 +56,6 @@ set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 include_directories(
 	"src"
 	"test"
-	"vendor/json/include"
 )
 
 # Define source files

README.org

@@ -22,6 +22,7 @@ This package is available through the AUR, linked here [[https://aur.archlinux.o
 + (make) ~cmake~
 + (make) ~git~
 + (make) ~gzip~
++ (make) ~nlohmann-json~ [[https://archlinux.org/packages/community/any/nlohmann-json/][arch]], [[https://packages.debian.org/search?keywords=nlohmann-json][debian]], [[https://packages.ubuntu.com/search?keywords=nlohmann-json][ubuntu]]
 + (optional) ~grep~
 + (optional) ~pacman-contrib~
 + (optional) ~apt-cache~, ~apt-mark~, ~dpkg-query~

src/config.cpp

@@ -11,7 +11,7 @@
 #include <string>
 #include <vector>
 
-#include "nlohmann/json.hpp"
+#include <nlohmann/json.hpp>
 
 #include "config.h"