Add new concept json and concept exercise githup-api (#694)

* add exercise code and tests

* rest of the  concept exercise

* add concept

* use triple quotes for all the examples

* add paragraph about newcommers impressions

* split section about json data to core/collections

* make and generate introduction

* configlet fmt

Author: jiegillet

concepts/json/.meta/config.json

@@ -0,0 +1,7 @@
+{
+  "blurb": "Learn how to parse and write JSON content",
+  "authors": [
+    "jiegillet"
+  ],
+  "contributors": []
+}