add nlohmann/json

this will conflict with a change in the http branch, but i dont care
right now

.gitmodules

@@ -21,4 +21,7 @@
 	url = https://github.com/nih-at/libzip
 [submodule "deps/cpp-httplib"]
 	path = deps/cpp-httplib
-	url = https://github.com/yhirose/cpp-httplib
+	url = https://github.com/yhirose/cpp-httplib
+[submodule "deps/json"]
+	path = deps/json
+	url = https://github.com/nlohmann/json