Add nlohmann-json

INDEX.lmi

@@ -3,4 +3,5 @@ Type: Index
 Package: taywee-args; external/taywee-args.lmp
 Package: spdlog; external/spdlog.lmp
 Package: ms-third; external/ms-third.lmp
-Package: ranges-v3; external/ranges-v3.lmp
+Package: ranges-v3; external/ranges-v3.lmp
+Package: nlohmann-json; external/nlohmann-json.lmp

external/nlohmann-json.lml

@@ -0,0 +1,4 @@
+Type: Library
+Name: json
+
+Include-Path: nlohmann-json/include

external/nlohmann-json.lmp

@@ -0,0 +1,5 @@
+Type: Package
+Name: nlohmann-json
+Namespace: nlohmann
+
+Library: nlohmann-json.lml

library.dds

@@ -4,3 +4,4 @@ Uses: taywee/args
 Uses: spdlog/spdlog
 Uses: ms/wil
 Uses: Niebler/ranges-v3
+Uses: nlohmann/json

peru.yaml

@@ -3,6 +3,7 @@ imports:
   taywee-args: external/taywee-args
   wil: external/wil
   ranges-v3: external/ranges-v3
+  nlohmann-json: external/nlohmann-json/include/nlohmann
 
 git module spdlog:
   url: https://github.com/gabime/spdlog.git
@@ -25,3 +26,6 @@ git module ranges-v3:
   url: https://github.com/ericniebler/range-v3.git
   rev: 0.9.1
   pick: include/
+
+curl module nlohmann-json:
+  url: https://raw.githubusercontent.com/nlohmann/json/v3.7.0/single_include/nlohmann/json.hpp