Don't use JsonBuffer to create or parse objects and arrays.

* Added DynamicJsonArray and StaticJsonArray
* Added DynamicJsonObject and StaticJsonObject
* Added DynamicJsonVariant and StaticJsonVariant
* Added deserializeJson()
* Removed JsonBuffer::parseArray(), parseObject() and parse()
* Removed JsonBuffer::createArray() and createObject()

test/JsonVariant/is.cpp

@@ -72,7 +72,8 @@ TEST_CASE("JsonVariant::is()") {
   DynamicJsonBuffer jsonBuffer;
 
   SECTION("JsonArray") {
-    checkIsArray(jsonBuffer.createArray());
+    DynamicJsonArray array;
+    checkIsArray(array);
   }
 
   SECTION("bool") {